Eric Sideman's Pest Report

July 15, 2001

The crop condition is generally good around the state, if you have not been hit by armyworm or have not been in an area that has been skirted around by the numerous showers this week. Most growers now have plenty of water in the soil, but I have heard from a few who are still very dry. The big problem I have seen is weeds. Weeds germinated late this year and many growers thought they had very good control until all of a sudden, WHAM. All the fields at once had a bloom of crab grass and other annual weeds and there was not time to get to them all.

PHYTOPHTHORA WATCH (Modified from UMASS Newsletter)

We have had enough rain in the past week that low-lying areas in some fields may have had standing water for periods of time after heavy rains. In fields with crops that are susceptible to Phytophthora capsicii -which includes all the vine crops, pepper, tomato, and eggplant - these low spots are sites where a Phytophthora outbreak could begin. We know that many soils around the state are infected with Phytophthora spores from outbreaks in past years. These resting spores (oospores) are most likely to germinate when there are alternating periods of dry soil followed by saturation. Standing water (or fully saturated soil) and warm temperatures are ideal conditions for spores (both oospores and sporangia) to germinate and release the swimming zoospores. These mobile spores will travel through the soil water, in surface water, in splashing water, or aerially in windblown rain to infect leaves, roots, crowns, or fruit. Once established, the fungus produces a yeast-like growth that contains many sporangia. Sporangia are lemon-shaped structures that cause new infections as they disperse into the rest of the field.

The best control for this disease is to never allow that initial infection to start. Take measures to reduce standing water by subsoiling between beds or rows, and removing soil barriers that might keep water from draining out of the field. Scout low-lying pockets for signs of infection. In pepper, look for black lesions on the stem or circular, grayish brown lesions on leaves. In cucurbits, look for seedling damping-off, crown rot which causes the whole plant to collapse and die in a short period of time; or dieback on the growing tip. The initial symptoms of fruit rot are a water-soaked or depressed spot, often on the underside of the fruit or near the stem. If you suspect you may have this disease, call the UMaine Pest Management Office (1 800 287 0279) to arrange for sending a sample.

LEAF HOPPER

I have now seen adult potato leaf hoppers on beans. This is a very destructive pest that some years comes into the state in such numbers that some crops like beans and potatoes are totally destroyed. They do not overwinter in Maine but leap frog their way up from the gulf coast each summer, sometimes making it in big numbers and sometimes not. Be on the lookout and let me know if you see them in large numbers.

The potato leaf hopper favors alfalfa, beans, strawberries and potatoes. It is a bug that sucks the plant juices. The feeding causes curling, stunting and dwarfing accompanied by a yellowing, browning or blighting of the foliage know as hopperburn or tipburn because the damage is first seen at the leaf tips working inwards.

The leaf hopper is small (3mm), pale green and wedge shaped. They are very fast and often not seen by the grower until the damage is so great that the farmer finally looks carefully. It is too late then. Look now and continue looking on a regular basis. The best way to spot them is to run your hand over the top of the crop lightly brushing the leaves. If you have them you will see them hop quickly. If you have them bad you may see a cloud. Find one that lands and identify it. (Tarnished plant bugs also may flitter around). A better way to find the leaf hopper is with a sweep net if you have one. Later in the year you will see the nymphs, especially on the underside of leaves. They are easy to identify because they can run backwards and sideways. When you spray be sure to hit these too.

Crop rotation will not help control leaf hoppers. The only organic control that works for the leaf hopper is a concentrated pyrethrum spray such as Pyrenone or Pyronyl *, which I know that Johnnys went out of there way to find. Only use these if you have a pest that needs it. These are broad spectrum, harsh pesticides that kill plenty of beneficial insects too.

· NOTE: BOTH PYRENONE AND PYRONYL HAVE PBO IN THEM AND THIS WILL NOT BE PERMITTED BY ANY ORGANIC STANDARDS NEXT YEAR. ALSO, IF YOU ARE SHIPPING ORGANIC PRODUCT OUT OF STATE DO NOT USE PRODUCTS WITH PBO BECAUSE MANY CERTIFIERS DO NOT PERMIT IT NOW.

ARMYWORM

The armyworms are nearing the end of the first generation as most of the caterpillars are full grown now and will go into the soil to pupate and turn into moths. For many growers it has been terrible. I have heard of total crop losses on very large scales.

There will be a second generation, but the accepted prediction is that it will not be nearly as damaging as this year's first generation. But, keep your eyes out and let me know if you see them. Watch peppers, I hear that the second generation will go after crops other than grasses especially peppers. See the last Pest Report for more information on armyworm.

TARNISHED PLANT BUG

The tarnished plant bug is out big time this year. Damage is seen in broccoli as brown beads, in lettuce as browning on the ribs, and in peppers and eggplant as no or very little fruit on what otherwise look like good plants.

The tarnished plant bug is a flat, quarter inch long bug that is shy and either runs to hide or flies away quickly when disturbed. Its back is mottled white and a dull, brassy yellow with touches of black. Nymphs look similar to adults but have little wings and cannot fly. It sucks plant juices from young plant tissue and injects a toxin at the same time, especially in buds leading to deformed fruit (or no fruit at all).

Control is very difficult if not impossible. They are very numerous and feed on about 300 different plant species so even if you kill them on your crop with a spray of pyrethrum new ones will quickly appear. Covering eggplant and peppers with floating row covers gives very good results. There is a parasite that was released by the USDA and it is spreading. If anyone knows of a good control please let us know.

SCARAB BEETLES (JAPANESE BEETLES AND RELATIVES) (modified from Umass Newsleter)

Japanese beetles are emerging now and congregating in various crops and non-crop habitats. These are one of three species of the scarab beetles which have been observed this season in vegetables: 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.

Oriental beetles normally fly at night but may occasionally be seen at dusk or in the soil when weeding. The beetles are just a little smaller than Japanese beetles, and usually are a rather mottled gray with black splotches. (Occasionally an individual will be almost all black or almost all gray.)

Asiatic garden beetles are about half as long as a Japanese beetle adult, and somewhat more "plump" in appearance. They are reddish-brown or copper-colored. They often are found near roots of plants when one is weeding.

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 favorite trees (such as locust or willow).

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 in early July in Maine mostly south of Bangor. The adults are active in daylight and begin feeding on many different kinds of plants, including roses, grapes, lindens, purple-leafed plums, and crabapples. In vegetables, they can be found in many crops including corn, peppers, green beans, collards, basil, soy beans and other herbs and greens.

The females return to the soil (often in or near wide expanses of turfgrass) and 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 begin to 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.

Japanese beetles are the most common and widely distributed scarab species in New England and until about 10 years, they were the primary grub species in most of New England. Recently, we are also finding some relatively new "imports" into the region. The Oriental beetle is found throughout Connecticut and Rhode Island, as well as Long Island. More recently we have found several populations in the Connecticut River Valley. The biology of this insect is very similar to that of the Japanese beetle. However, the oriental beetle tends to be less sensitive to several of the insecticides that are commonly used in turf. The Asiatic garden beetle (AGB) is gradually becoming a nuisance in many areas throughout New England. While we are not sure what is going on, we suspect that it is not particularly vulnerable to insecticides, so when other grubs are killed, the AGB moves into the vacated niche.

Control

There are usually large populations of Japanese beetle grubs in sod ground before any damage to the sod is noticed. Some lawn lovers may want to try parasitic nematodes or the milky spore disease, but controlling the grubs in nearby sod ground will do little for controlling the adults in vegetable, because they are very good fliers and very numerous. In vegetables, managing the grub stage may not be feasible since the grubs are most likely feeding elsewhere.

The beetle traps that attract the adults and catch them usually does not work for vegetable growers because they attract adults from very far away...millions of them...but they do not catch every one. The best control on small scale operations is to knock the adults into a jar of soapy water every morning. Rotenone is an option for controlling adults. Insecticide should be applied in the evening for night-feeding beetles, or in the morning for day-feeders.