|| MOFGA's 2007 Pest Reports - Compiled by Eric Sideman, PhD
|July 16 | July 3 | June 19 | June 4 | May 25 | May 7|
|POTATO LEAF HOPPER: The potato leaf hopper is wide spread now in Maine on potatoes, beans and strawberries. Check the July 3 Pest Report for details.|
BLACK ROT OF BRASSICAS: Black rot is a potentially very destructive disease that effects all Brassica vegetables. It can appear on plants at any growth stage. The symptom on true leaves is yellow, vaguely V-shaped areas that sort of follow leaf veins. As the lesion expands the tissue wilts and eventually becomes brownish and dry. The infection may move up or down the plant in the vascular tissue and such a systemic infection may produce scattered yellow lesions on leaves anywhere on the plant. Veins of infected leaves turn black.
Black rot is caused by a bacteria called Xanthomonas campestris. The pathogen survives from season to season on seed and in diseased crop residue. It also can survive in soil for a month or two. Very few infected seeds can lead to a crop failure as the disease can spread very quickly under the right conditions in splashing water, wind, insects and farm workers. Long distance spread is by seed and transplants.
Key to avoiding the disease is to use clean seed. A hot water treatment is effective but it needs to be done carefully (see the Resource Guide for Organic Insect and Disease Management for details, which is available from MOFGA or at https://www.nysaes.cornell.edu/store/catalog/.
Crop rotation is important. If you have this problem avoid planting Brassicas for 2 years in that field and be sure to manage Brassica weeds. Sanitation is also important. Destroy crop residue after harvest. If the disease is present do not plant a successive crop into that soil. Cull piles should be composted or destroyed. Do not use manure from livestock that have been fed diseased Brassicas on fields intended from Brassica crops.
SWEET CORN SITUATION: (Reprinted from UMaine Sweet Corn IPM Newsletter No. 2). Corn planted on early ground and through plastic mulch in southern Maine is now in silk. Many stands around the state are uneven, and growers have been watering as much as possible to keep up growth through the recent dry spell. Late plantings are in whorl to pre-tassel. Fertilizer burn from sidedressing has been noticeable in some fields, probably worse this year due to the lack of water. Once corn starts silking we need to be even more alert to pest issues. All three of the major insect pests can enter the silk channels and feed on the ears without leaving visible damage on the plant. Therefore, we must respond to moth captures in pheromone traps to be able to adequately protect the crop.
European Corn Borer: Pheromone trap catches indicate that we continue to experience a significant flight of European corn borer moths, with over 300 caught in one trap last week. We are finding more larvae feeding on the foliage and tassels this week. From the pre-tassel stage to silking stages, the control threshold is 15% of plants showing damage. Sprays during the pre-tassel stage reduce the opportunity for larvae to move into the stalks and ears of the plant. Several fields were over threshold for feeding injury this week for pretassel to silking corn, and sprays were recommended. When corn reaches the silk stage sprays may be based on the number of corn borer moths caught in pheromone traps rather than just feeding injury. European corn borer moths will lay eggs on flag leaves of silking corn and the larvae can move into the ears without leaving any visible feeding injury that would be noticed when scouting. Therefore, if more than five moths are caught in a week in a field with silking corn, a spray will be recommended. Sprays to protect silking corn from European corn borer were recommended in Auburn, Dayton, New Gloucester, Nobleboro and Wayne.
Corn Earworm: We continue to catch a few corn earworm moths around the state, mostly as single moths in traps, and/or in fields that are not yet silking. Therefore we have not yet recommended a spray for earworm in any field, but we will be keeping a close eye on this in the coming weeks. The risk of an infestation will increase greatly if our weather patterns change to bring fronts up from the southern states, which tend to carry the moths with them. The arrival of this pest is only aconcern for corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm.
Fall Armyworm: We caught one fall armyworm in a New Gloucester pheromone trap this week. While this is not yet cause for alarm, it may indicate that we can expect an early arrival of this pest. We have not yet found any feeding injury from larvae. Pheromone trap catches will indicate if this pest presents a threat to silking corn, however corn will usually be on a spray program for corn earworm when fall armyworm is present, and both insects would be controlled.
IMPORTED CABBAGE WORM: The white butterflies are flying all around the cabbage family plants now and laying eggs, and the larvae (green caterpillars) are chewing holes in the leaves. If you have heading broccoli you must know your customers because some folks are really turned off by the critters floating to the top of the water in the cooking pot. You may want to spray that even though the crop is beyond risk.
This pest overwinters as a pupa and there are 3-4 generations per year. This means that once you start seeing the butterfly you should start scouting for the caterpillar in about a week. Bt (Dipel 2X or Dipel DF) or Entrust work very well in controlling the caterpillar. None of these materials lasts in the field and so should only be sprayed when the caterpillars are there in large enough numbers to warrant it.
Destroy or bury crop residue after harvest so as not to allow the caterpillars to continue to feed and complete their life history and thus a larger second generation.
BACTERIAL DISEASES OF TOMATO - UPDATE 2007: (Modified from a report in from the Umass Vegetable Newsletter). Three bacterial diseases affect tomato crops-Bacterial Spot (Xanthomonas campestris pv. vesicatora), Bacterial Speck (Pseudomonas syringae pv tomato), and Bacterial Canker (Clavibacter michiganensis pv michiganensis).
Bacterial spot caused by Xanthomonas campestris pv. vesicatora (Xcv) is present wherever tomato and peppers are grown. In general, Xanthomonas pathovars have narrow host ranges. Xcv consists of different strains that vary in their pathogenicity to tomato, pepper, and solanaceous weeds. The bacterium is able to survive on tomato volunteers and can overwinter in diseased plant debris. Seed is an important mechanism for survival and dissemination of Xcv. Disease development is favored by temperatures between 80 and 90 F and by heavy rainfall. The bacterium is spread by wind-driven rain, workers, farm machinery, and aerosols. It penetrates through stomates and wounds created by insects, wind-driven sand, and tools. Xcv affects all aboveground plant parts. On leaves, the spots are generally brown, circular, and water-soaked. Bacterial spot lesions do not have concentric zones or a prominent halo. When conditions are optimal for disease development, spots can coalesce to form long, dark streaks. A general yellowing may appear on foliage with many lesions giving the plants a scorched appearance, and the plants may exhibit severe epinasty. Only green tomato fruit is susceptible to infection and lesions are quite distinct, beginning as minute, slightly raised blisters with a halo that resemble the birds-eye spot caused by Clavibacter michiganense (bacterial canker). As lesions enlarge, they loose their halo and become brown, raised, and scab-like. Lesions on ripe pepper fruit may be scab-like or sunken.
Bacterial speck occurs on tomato not pepper. It is a cosmopolitan disease, generally of minor concern, favored by low temperatures and high moisture. The bacterium Pseudomonas syringae pv tomato causes a fruit spot and foliage blight. This bacterium is also seedborne, spreads within fields in the same manner as bacterial spot, and may persist in weed species. Lesions on leaves are round and dark brown to black with a halo that develops with time. Spots may coalesce, killing large areas of tissue. On fruit, small (1/16 inch), dark spots or specks develop with the tissue around them often more intensely green than unaffected areas.
Bacterial canker (Clavibacter michiganensis pv michiganensis) is one of the most destructive tomato diseases in Massachusetts. Initial symptoms are the result of primary, systemic infection and first affect the lower leaves causing leaf curling, wilting, chlorosis, and shriveling. In advanced stages, the pathogen spreads throughout the plant and causes poor growth, wilt, and plant death. Foliage throughout the canopy wilts, yellows, turns brown, and collapses. Stems can split resulting in open breaks or cankers and stems break easily. Secondary infections occur from rain splash onto foliage, stems, and fruit. Spots occur on green fruit and are very characteristic: white to yellow spots, 3-4 mm with raised brown centers ("bird¹s eye spots").
Three key principles for preventing losses to bacterial diseases are:
1. Start with certified, disease-free seed or treat seed with hot water, hydrochloric acid, calcium hypochlorite, or other recommended materials. See the fact sheet entitled, Preventing Bacterial Diseases of Vegetables with Hot-water Seed Treatment for further details at www.umassvegetable.org.
2. Control bacterial populations that may be present on the leaf surface of transplants in the greenhouse. Young transplants may not display symptoms of bacterial diseases. Inspect and remove suspect transplants. Lower the water
pressure in irrigation equipment to avoid damaging leaves. Avoid the practice of mowing transplants to regulate transplant height.
3. Plant into a clean field. Promptly incorporate crop debris after harvest. Rotate to a non-host crop before returning to tomato and do not allow volunteer tomato or weed hosts to survive.
Research at the University of Michigan has shown that: 1) the pathogen can move readily from infected plants onto clean plants in the course of regular greenhouse activities, and 2) carryover in the greenhouse from one season to the next may not be as important as was once thought. In one experiment, seedlings that carried systemic infections with bacterial canker were placed in known locations in a grid of transplants in the greenhouse. Watering was from hand-held sprinklers no special precautions were taken to prevent disease spread. Plants nearest the infected plants developed bacterial canker symptoms (wilting) and died in the greenhouse. Many other plants showed no symptoms in the greenhouse, but the bacteria could be found residing on the surface of the leaves. When these healthy-looking plants were set out in the field, they developed symptoms during the season and the yield losses were serious. This type of infection -- bacteria that enter from the surface of the leaf through natural leaf openings or wounds -- causes the ³marginal scorch² symptoms that are so common in Massachusetts. Once the bacteria enters the plant -- which could occur in the greenhouse or in the field -- it can take anywhere from 7 to 84 days for symptoms to appear.
If infected plants are present, the movement of bacteria from one plant to another during normal watering, handling, and ventilating activities occurs readily. Controlling the bacteria at this stage can prevent yield losses. Bacteria on the surface of transplants can be effectively controlled by sprays of copper hydroxide. Kocide DF is labeled for greenhouse use on tomato.
Avoid working in fields when bacterial diseases are present and the fields are wet.
Rotate your tomatoes to a different field. Setting clean transplants into a field where infected tomato was grown the previous year will result in early infection and reduced yields. Bacteria survive in the field as long as there is any infected crop debris. They persist longer in debris on the surface than in buried debris. Plowing after harvest will help to speed up the decomposition. Keep each field out of tomato (and related crops such as potato and eggplant) for two to three years. Avoid using overhead sprinkler irrigation in the field. Use new stakes or stakes that have been cleaned and disinfected. Periodically and regularly sanitize tools such as clippers and pruning shears with an approved disinfectant during field operation.
Prevention is cost-effective. All of these tactics focus on prevention -- ensuring that disease-free plants go out into a ³clean² environment. Bacterial disease outbreaks in the field require regular sprays with a copper with limited success. Prevention strategies are both the least expensive and the most effective way to treat these diseases. -- Dr. Robert Wick, Dept of Plant, Soil & Insect Sciences, University of Massachusetts, M. Bess Dicklow, UMass Extension Plant Diagnostic Lab.
SCARAB BEETLE UPDATE: JAPANESE, ORIENTAL AND ASIATIC GARDEN BEETLES ARE ACTIVE: (Modified from a Report in the Umass Vegetable Newsletter). Japanese Beetles have emerged and are showing up in various crops and non-crop habitats. Oriental Beetles are also active and, though less damaging, may appear in vegetable fields as well. Asiatic Garden Beetles become evident mostly through their damage, because they feed at night. All species are feeding and starting to lay eggs now.
There are four species of scarab beetles that are common in New England turf, fruit and vegetable crops. These were all introduced to the US. Japanese beetles are the most common and widely distributed but Oriental and Asiatic Garden beetles are expanding their range and activity. Below are brief descriptions.
JAPANESE BEETLE adults are about half an inch long, with a metallic green head. The wings are shiny copper or bronze color, and there are a few tufts of white "fur" along the side of each wing when it is folded back over the body. The adults are active in daylight and feed on many different kinds of trees, fruit and flower crops. Fruit and ornamental plants are preferred, but beetles can congregate in vegetables also. In vegetables, adults can cause silk clipping in corn, and leaf damage in sweet basil, collards, other greens, green beans, eggplant, asparagus, rhubarb, and peppers. Though numbers may be high, there is no need to treat unless actual feeding damage is significant. In corn, if there are more than two Japanese beetles per ear and corn is less than 50% pollinated, an application may be warranted to reduce clipping and ensure adequate pollination.
ASIATIC GARDEN BEETLES are about half as long as a Japanese beetle adult, and somewhat more ³plump² or domed in appearance. They are reddish-brown or copper-colored. They often are found near roots of plants when one is weeding. Adults tend to cause more damage to vegetable crops than Oriental Beetle, but less than Japanese beetles. Because they feed at night, one may find damage without seeing the beetles. During the day they hide in the loose soil or mulch around the base of the plants. Scout with a flashlight at night, or sift through soil to find them. Larvae feed on beet, carrot, corn, lettuce, onion, Swiss chard and strawberry. Adults feed on carrot, beet, parsnip, pepper and turnip. One grower reported heavy beetle feeding on peppers that were held under row cover through the end of June: this could be the result of Asiatic garden beetles that emerged under the cover. He could not find beetles, only damage. Beware the events that occur under row cover while unsuspecting farmers are looking the other way!
ORIENTAL BEETLES fly at night, but are very active during the day as well. The beetles are smaller than Japanese beetles, and usually are a rather mottled gray with black splotches. The pattern and color varies. Occasionally an individual will be almost all black or almost all gray. The antennae are branched and are quite striking if you take a close look. Oriental beetles have a long flight period through early August and are very mobile. Adults tend not to feed heavily in vegetable crop foliage. Grub damage may be worse in drought years and in weedy fields, but is not commonly a problem in vegetable fields and crops, though this is not well studied.
A fourth species may also be found: EUROPEAN CHAFERS, which are slightly larger than Japanese beetles and are a fairly dull brown or tan in color. They are night fliers but can be seen in large numbers just at sunset, when they congregate in large numbers in favorite trees (such as locust or willow). Adults are not foliage feeders and grubs are mostly a turf problem.
LIFE CYCLE. The life cycle of the Japanese beetle fits most of the species of grubs we encounter in New England, with minor variations depending on the species and the location. They have a one-year life cycle, with adults emerging from the soil in early July in most of Massachusetts (later farther north) to feed and mate. The females burrow into the soil (often in or near wide expanses of grass or sod) to lay eggs, usually beginning in late July. Eggs hatch into tiny grubs (cream-colored larvae, C-shaped, with brown heads). The first grubs usually appear around late July or early August and begin feeding on roots of grasses and other plants (especially corn). After about two weeks of feeding, the grubs molt to a second "instar", and feed for another three weeks. The grubs molt once more, to the "third instar" (or large grub) around the middle of September, and continue feeding until the soils begin to cool down. In late fall the grubs migrate downward through the soil profile, staying below the frost line throughout the winter. In the spring as the soils warm up, the grubs move back into the root zone and resume feeding for about six weeks. By the middle of June, most grubs have completed their feeding requirements and pupate (still in the soil) for about a week before emerging as new young adults.
CONTROLS. There are not many controls for organic growers to choose from. Beneficial nematodes work fairly well on the grubs if there before the population explodes, but for vegetable grower the adults are the critters that cause most damage and they are good fliers so your control of grubs in your sod fields will not likely reduce the damage. Neem and pyrethrum offer fair control of the adults. - R. Hazzard, adapted from Pat Vittum, Turf Entomologist, UMass, Beth Bishop, Michigan State University, Michael Seagraves, Cornell Cooperative Extension, and Ann Hazelrig, University of Vermont
STRIPED CUCUMBER BEETLE: All over the Northeast, striped cucumber beetle is our most serious early-season pest in vine crops. These beetles spend the winter in plant debris on field edges and move rapidly into the field with the emergence of cucurbit crops and the onset of warm days. Densities can be very high, especially in non-rotated fields or close to last year's cucurbit crops. Adult feeding on cotyledons and young leaves can cause stand reduction and delayed plant growth. More importantly, the striped cucumber beetle vectors Erwinia tracheiphila, the causal agent of bacterial wilt. This disease overwinters within the beetle and is transmitted by contact of beetle feces with the open wounds in leaf tissue caused by beetle feeding. Bacteria multiply and block the vascular system of the plant, causing vines to wilt. This disease can be effectively managed only by preventing feeding by the beetle. Vine crops vary greatly in their susceptibility to wilt.
Early season infection. Pumpkin plants at the cotyledon and first 1-2 leaf stage are more susceptible to infection with bacterial wilt than older plants, and disease transmission is low after about the 4-leaf stage. Wilt development is strongly influenced by the dose of the pathogen that the plants receive. Typically, only a relatively small proportion (1-10%) of overwintering beetles carry the Erwinia pathogen and are able to infect plants. The higher beetle density during early plant growth, the more severe the incidence of wilt. Beetles that discover a host plant will release an aggregation pheromone that calls others to their spot. Groups of beetles feeding, wounding and defecating on a single plant are more likely to transmit disease, acquire the pathogen, and transmit it to other plants.
Thresholds and foliar controls. Beetle numbers should be kept low, especially before the 5-leaf stage. Crop rotation to a field at a distance from last year's cucurbits reduces beetle numbers significantly and may eliminate the need for controls. Beetle numbers tend to build up when vine crops are planted in the same or nearby fields year after year. Conventional IPM systems have relied on scouting frequently (at least twice per week) and treating after beetles colonize the field. To prevent bacterial wilt, we recommend that beetles should not be allowed to exceed one beetle for every 2 plants in susceptible crops. This is a lower threshold than is needed to prevent significant foliar damage. Less wilt-susceptible crops will tolerate one or two beetles per plant without yield losses. Proper timing can be difficult: growers have to be ready to respond quickly in a very busy time of the season, and weather or field conditions can delay sprays. However, foliar sprays remain a viable option (see below).
Row covers are being used by many growers of curcubits to prevent early season attack by the cucumber beetle. Remember, the row covers need to be removed to weed periodically, and removed for the season when flowers appear to allow pollination.
Scouting and using foliar sprays: Look for signs of feeding on the underside of leaves, especially the cotyledons. Beetles are often found underneath leaves or in cracks in the soil. Check sets of 5 plants in at least five areas of the field (25 plants total), counting number of beetles on or near the plant. This can be done in about 15-20 minutes. Check field edges for hot spots. Beetles often colonize from field edges and numbers will be higher in the first rows near a woods or fallow area. Border treatments or border trap crops may help reduce infestation of the whole field. See the 2002-2003 New England Vegetable Management Guide for specific materials. (Don't have one? Call your local Extension office to order your copy).
When to spray? Controlling cucumber beetles in the cotyledon to 5 leaf stage is the only way to preventing bacterial wilt. For susceptible crops such as cucumber, summer squash and zucchini, muskmelon, gourds, and some winter squashes and pumpkins, lower thresholds are needed. Do not allow numbers to exceed 1 beetle per two plants. The time between first arrival of beetles and that threshold can be short, so keep an eye on fields once you see any beetles and spray within 24 hours of reaching threshold.
Controls: For organic growers, kaolin (Surround WP) provides an option. It is best applied by dipping seedlings before transplanting. Pyrethrin (Pyganic Crop Spray 5.0 EC) is another option but to me since it is a broad spectrum pesticide is muh less attractive. Use as a last resort only. Perimeter trap crops (see below) are another option. NOTE: available Rotenone products do not meet inert ingredient guidelines under the National Organic Program. For growers using Surround, here are some suggestions:
Most important is to clean up fields early in fall after harvest and reduce overwintering sites. -- Modified from a 2002 report by Ruth Hazzard
- Apply before beetles arrive. This acts as a repellent and anti-feedent so must be present before damage is done.
- If you are using transplants, apply before setting them out. This saves time and materials.
- With direct-seeded crops, apply as soon as seedlings emerge if beetles are active.
- Ensure good coverage of the foliage (it will look like it was sprayed with white latex paint), including, if possible, the undersides of leaves (not easy when cotyledons are close to the ground).
- Reapply after a heavy rain.
- When mixing, add the powder to water and allow it to settle slowly. Once the powder is fully wet, agitate gently. This reduces clumping. One approach is to mix a more concentrated slurry in a bucket and then add the slurry to the tank, as the dry powder could cake if added directly to the tank mix. Continuous agitation is needed.
- Although kaolin is safe in terms of skin exposure or ingestion, handlers should take precautions to avoid breathing the powder. Wear a respirator or mask when mixing and spraying.
PERIMETER TRAP CROPPING FOR CUCUMBER BEETLE MANAGEMENT: Trap crops are used to protect the main cash crop from a pest or complex of pests. The trap crop can be a different plant species, variety, or just a different growth stage of the same species as the main crop, as long as it is more attractive to the pests when they are present. Perimeter Trap Cropping involves planting the attractive plant species so that it completely encircles the main crop like fortress walls. A trap crop barrier on all sides is useful when it is necessary to protect the crop from a pest attack that may come from several or unknown directions. This technique works best against pests that tend to damage the crop along the edge of the field (at least initially) - such as striped cucumber beetle.
Perimeter Trap. Cropping functions by concentrating and/or killing the pest in the border area, while reducing pest numbers and disease spread on the unsprayed cash crop in the center and by preserving natural enemies. Perimeter Trap Cropping often eliminates the use of broad-spectrum pesticides on the cash crop, which helps preserve natural enemies and helps prevent resurgence of the primary pest population, secondary pest outbreaks and additional spraying to solve these "man-made" problems. Perimeter Trap Cropping often results in improved crop quality and dramatic pesticide savings. Less spraying usually translates into lower costs.
Blue Hubbard around yellow summer squash. In 2002, Connecticut researchers attempted to stop cucumber beetles and squash vine borers damage on summer squash using Blue Hubbard as a perimeter trap crop. Blue Hubbard was chosen because it is highly attractive to beetles, grows fast, and is not susceptible to bacterial wilt so it does not serve as a reservoir of wilt for the rest of the field. In the 2002 trials, over 94% of the cucumber beetles in the experiment were on plants in the perimeter. Beetle populations on the unsprayed main crop in the center were reduced by up to 95%. In addition, spraying the perimeter trap crop reduced squash vine borer infestation on the unsprayed summer squash within by 88%. Six commercial cucurbit growers successfully employed the technique in 2002. All the growers improved their pes control and reduced crop damage using Perimeter Trap Cropping, and all said they would continue to use trap crops in the future.
How to use perimeter trap cropping in yellow and green summer squash - or other vine crops. A number of growers in CT and MA are testing Perimeter Trap Cropping in summer squash and butternut this season. You may be interested in trying it, or come to summer twilight meetings to learn more about it. Here are some suggestions if you want to try it:
PTC can also be used to reduce pepper maggot infestations in pepper - with a ring of cherry peppers around bell peppers - and diamondback moth in cabbage - using collards as the trap crop. For more information visit the UConn website at http://www.hort.uconn.edu/ipm/veg/htms/trpcrops.htm
- Use a rotated field where cucumber beetle populations are not extremely high.
- Plant the trap crop earlier or at the same time as the main crop.
- Use the same in-row and between row spacing to plant the main crop and the perimeter trap crop row (or rows) of Blue Hubbard. Plant the outside rows along the length of the block by machine. Trap crop plants at the end of each row can be placed by hand or by machine (drive across the rows). Don't worry if all the Blue Hubbard plants don't line up with the main crop rows or are killed between rows by tractor tires. As long as most of the border plants survive on all sides of the field, without major gaps (>15 ft), the barrier should still function.
- Scout the trap crop at least twice weekly and spray the border with an effective insecticide (Pyganic) as soon as beetles are found. Don't wait for beetles to build up in the borders. It is important to maintain healthy border plants and to prevent redistribution throughout the field. However, even without border sprays, PTC reduces beetles in the main crop. Scout again to determine if repeat sprays are needed in the border.
- Don't mix another, highly attractive vine crop inside the border. Or, if you do, monitor it closely to determine if sprays are needed on that main crop. For example, zucchini is more attractive than summer squash and may need to be sprayed even if it is inside a blue hubbard perimeter.
- Where heavy infestations might be expected, such as borders along woods where beetles may have overwinter, use a wider perimeter of 2-3 rows.
- Watch for more details on twilight meetings at demonstration farms in Connecticut and Mass!
Adapted from PTC for Yellow and Green Summer Squash and Perimeter Trap Cropping Works!, by T Jude Boucher and Robert Durgy, University of Connecticut Cooperative Extension System.
July 16 | Page 1 of 6 | July 3