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  You are here:  PublicationsPest ReportsPest Reports - 2006   
 MOFGA's 2006 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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The wet weather continues and it is time to start thinking about diseases that were a problem on your farm last year that may be hard to avoid this year, especially if your crop rotation and sanitation were not what they should have been. There was a very nice warm string of days just at the right time to get the warm weather seedlings out in late May, but now they have been sitting in wet soil with wet leaves and the cool air has delayed growth. I think this may be a year of spots.

Tomato Spots: The three most common problems with tomatoes grown in the field in Maine are Early Blight, Bacterial (Spot and Speck) and Septoria Leaf Spot.

Bacterial Speck starts as dark brown to black spots on leaves that later develop yellow halos around the area effected. On the fruit black specks develop that rarely get larger than 1 mm . Bacterial Spot starts as brownish, circular spots that may become as large as 3mm and irregular. The diseases may be seed borne and may be carried over in weeds. High humidity and low temperatures favor bacterial speck.

Early blight of tomato is caused by fungi and starts on the lower leaves as small circular spots that have a target appearance of concentric rings. Leaves develop yellow blighted areas as the spots enlarge. Later the tomato fruit may rot on the stem end. The disease is carried over on tomato residue in the soil and can be seed borne.

Septoria Leaf Spot is a fungal disease that starts as spots on the lower leaves that have a dark brown margin and a tan center, and no target appearance. Rapid defoliation can occur.

Crop rotation is the first line of defense from these problems. Sanitation is important. Do not grow tomatoes near cull piles of last year's crops. Trellising, staking, cages, etc help but remember to disinfect if they were used last year (a 12X dilution of household bleach is effective). Prune off diseased lower leaves, but it is especially important to disinfect tools if the problem is one of the bacterial diseases. Avoid working in the crops when they are wet. Scouting is going to be important this year. With this weather start early and if you decide to use a material, copper is probably the one most effective for us organic growers. If you decide to do it, start at the first sign of problems and you need to keep the new tissue covered.


Cucumber Beetle: I have had the first report of striped cucumber beetle. These 1/4 inch long, black and yellow beetles spend the winter sheltered under plant debris near and in the field where cucurbits were grown last year. The overwintered generation can zero in on newly planted seedlings and eat all of the leaf tissue in a day. Once the plants attain 4-5 true leaves they are more tolerant of the feeding, but the beetle still can transmit bacterial wilt and populations should be kept small.

Crop rotation and sanitation help a great deal in avoiding the overwintered generation. Floating row covers are very effective for protecting young plants. Remember to remove to weed and then take away when the crop flowers to allow pollination. Trap cropping is possible with this crop and pest (see the Resource Guide for details). Pyrethrum will kill the beetles, but they are good fliers and often take off and return when you leave. There have been good reports from growers using Surround sprayed on seedlings before transplanting.


Root Weevil Management
From info supplied by Richard Cowles, CT Agricultural Experiment. Station; Peter Shearer, Rutgers Cooperative Extension; and others

Despite the open winter, we have observed some plantings of strawberries infested with the grubs of black vine weevil and strawberry root weevil this spring. It is not too late to put on an application of nematodes to control the grubs (optimal timing is about mid-May but we have been so wet and cool that I bet it may still work). Two species of nematodes appear to offer the best control of root weevil grubs. Heterorhabditis bacteriophora (Hb) appears to be the best candidate for control of root weevils when the soil temperature is above 60 degrees ('J-3 Max Hb' from The Green Spot; 'GrubStake HB' from Integrated Biocontrol Systems; 'Larvanem' from Koppert Biologicals). Beneficial nematodes can also be applied in late summer (August 15 - September 1), and in that case, Steinernema feltiae ('Nemasys' from Griffin Greenhouse Supply, 'Gnat Not' from Integrated Biological Control Systems, 'Entonem' from Koppert Biological) should be considered in northern locations since it tolerates cooler soil temperatures and completes its life cycle quickly.

Once the grubs begin to pupate (usually early June) nematodes should not be applied, because they do not attack the adult (beetle) stage. Once the adults become active bifenthrin (Brigade) will provide some control if used at the highest labeled rates. The best timing for this spray is at night during the peak feeding activity of adults, before they start laying eggs, or about 1 week before harvest ends. Neem-based products containing azadiractin (such as Aza-Direct) may be acceptable for organic production, and while neem will not kill the adults it can disrupt egg-laying if applied at high rates at least twice.

Nematodes are living organisms and they can be killed if they are misapplied. Order nematodes ahead of time and be ready to apply them through a sprayer or irrigation soon after they arrive, refrigerating if delay is necessary. Do not apply nematodes using a sprayer with a piston pump. Use clean equipment, removing all screens finer than 50-mesh. Apply nematodes in early morning or evening in a high volume of water to already moist soil, pre-irrigating if needed. Apply another π inch of irrigation after application to wash them onto and into the soil. Although references suggest rates of several billion nematodes per acre, I found researchers and suppliers recommended 250 (if banded in the row) to 500 million per acre, at a cost of about $100 to 200 acre depending on volume and source. Ironically, nematodes probably work best in the worst weevil-infested fields. High populations of weevil larvae allow explosive growth in nematode populations, while low populations of larvae may not permit efficient nematode reproduction. Strawberry plants can recover their vigor remarkably well if crown feeding has not occurred and diseases haven't taken over the roots.

Root weevils cannot fly, so they infest new plantings by wandering into fields from surrounding weedy and woodland vegetation, or in large numbers from recently plowed, infested strawberry plantings. Even plantings several hundred feet away can become generally infested as a result of mass migration from plowed fields. A good rotation program with substantial distance between strawberry fields can help to manage root weevils. Also, when turning under old, infested strawberry plantings, it is critical to leave a row or two at the perimeter of the field as a trap crop to protect other plantings. Adult weevils will be intercepted in these rows before they leave the field and thus lay their eggs where the larvae will not do any damage. At the end of the season the trap rows should be turned under prior to planting winter rye. Do not spray the trap rows as this may repel weevils and result in more migration to other fields.

Some Beneficial Nematode Suppliers:
The Green Spot: 603-942-8925 or www.shopgreenmethods.com <http://www.shopgreenmethods.com >
Griffin Greenhouse Supplies: 978-851-4346 or www.griffins.com <http://www.griffins.com >
Integrated Biological Control Systems: 888-793-4227 or www.goodbug-shop.com <http://www.goodbug-shop.com >
Koppert Biologicals: 800-928-8827 or www.koppert.com <http://www.koppert.com >


SEEDCORN MAGGOT AND WIREWORM DAMAGE ON EARLY CUCURBIT TRANSPLANTS
Seedcorn maggot and wireworm are occasional pests on cucurbits. This year, it is possible that unusually warm temperatures in April followed by unusually cold and wet conditions in May has favored these pests. Pest alerts from Maine to Indiana have noted this pest as a problem. We have seen damage in Massachusetts in one early melon field. Symptoms are wilted plants and collapsed, rotting stems. These pests feed on the roots and bore into stems at the ground surface. They feed on the internal tissues and kill the plants. In the field if you find wilting plants and no clues of insect feeding or diseases on the aerial parts, then dig up the plant and check for seedcorn maggots and wireworms. The seedcorn maggot is yellowish-white, legless, with a pointed head and is about 1/4 inch long when fully grown. The wireworm is slender, jointed, usually hardshelled, with three pairs of legs, and tan brown in color. This week at a farm in the Connecticut River Valley, we found maggot pupae which are 1/4 inch long, oblong and tan or brown. Symptoms were noticed by the farmer last week, when maggots were actively feeding. Once maggots pupate, the damage is done. A new crop of adults will emerge in 7-14 days. Wireworms were also found, but maggots were most numerous. Cold conditions which inhibit crop growth but favor the maggots encourage this pest. Once a field is infested with seedcorn maggot or wireworm, not much can be done to cure the problem. Replanting decisions should be made based on estimates of the size of the maggots infesting the field. If the maggots are smaller than 1/4 inch long we recommend waiting 10 days to replant, if they are larger or equal to 1/4 inch long, plants can be replanted after 5 days. If wireworms are found, wait to replant until soil temperatures are above 70 degreesF. The field in which we found damage in Massachusetts was planted with melon transplants in early May, after tilling in a healthy cover crop, applying plastic with straw mulch between the rows, and putting row cover on hoops over the entire crop. It appears that the seedcorn maggot flies emerged, mated and laid eggs under the row cover or laid eggs after tillage but before transplanting. Maggot flies are attracted to the odors given off by the microorganism associated with decaying organic matter or diseased plants. For growers who want to improve their soil by incorporating large amounts of biomass in the spring, or use reduced tillage systems, it may be important to figure out how to avoid this risk. Waiting until soil is warm enough to encourage rapid germination and crop growth may help. Disking cover crops at least four weeks before planting may make them less attractive. As reported last week, seedcorn maggot attacks seeds and seedlings of many vegetable crops. After May and June this pest is rarely a problem.
Adapted a bit and reprinted from UMASS Notes from an article adapted by Ruth Hazzard from May 26, 2006 article by Dan Egel, Chris Gunter, and Frankie Lam, Vegetable Crops Hotline, Purdue University Cooperative Extension Service


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