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Pest Report - July 22, 2009

LATE BLIGHT: This is still the hot topic. It is now reported pretty much in all the corners of the state. Some areas are hot spots with lots of reports and others have only one or two growers reporting. We in Maine are not alone as it is all through New England and New York. Previous Pest Reports and Extension publications have dealt with how to handle it. Steve Johnson has recently put together a guideline for mixing small quantities to spray small areas, and also included a discussion of Worker Protection Standards for commercial growers. Download Steve's document.

LEAFHOPPERS: Potato Leafhoppers (PLH) have made it to Maine. I have just received a report of them in Wells on beans and they have been in southern New Hampshire for a while. They are likely to be moving north so be on the lookout. They also feed on potatoes, strawberries and alfalfa.. PLH does not over winter anywhere near here. They over winter way down south and leapfrog up here in mass migrations. The first to arrive are females, and they are usually carrying fertilized eggs when they get here. Then there are a few generations over the growing season before the cold north winter kills them.

The damage from leafhopper is catastrophic. The bug sucks the juice out of the plant and injects a toxin that clogs the food conducting tissue. The symptoms look like a disease after a while rather than insect damage. The leaves first get pale, then yellow and then brown from the edges. Then the plant dies. The symptoms are called hopper burn.

The adult PLH is very light green and wedge shaped and tiny (an eighth of an inch long). The best way to find them is to brush the plant and watch one of the white-looking bugs land. The nymphs are similar to the adult, but have no wings and are smaller and live on the underside of the leaves. If you disturb a nymph you will see it run and it can run sideways as fast as forward. This is a clue that you have PLH and not some other less harmful leafhopper.

The adults are flighty. When you brush your crop you will see them fly up. If there is a cloud, you are in trouble. If there is only one or two in a row of plants your crop will probably not be hurt badly. That is why researchers have developed a threshold before treatment is recommended. For example, on beans a population equal or exceeding an average of one nymph per leaf, or fifty adults per ten sweeps with a net means it is time to spray.

Crop rotation does nothing for you since they are coming from far away. Covering you crops with a row cover would work, but these crops are not the type that are usually covered. Effective insecticides are limited. The only material that I have seen work that is allowed in organic production is pyrethrum, so Pyganic is the recommendation that I make. However, it does not work that well. Spray late in the day or evening, get good coverage including the undersides of the leaves, and don't wait until it is too late.

Adult Mexican Bean Beetle.
(modified from an article By Ruth Hazzard - reprinted from the Umass Vegetable Newsletter). If you are having Mexican bean beetle problems now then next year plan for your management in the spring. It would have been good for me to give you that advice last winter. If these destructive insects have historically been a problem on your farm, you will very likely see them again every year. They may be pests on snap beans, soybeans, and lima beans. While they are not a pest on every farm, some farms report significant damage from these pests and have to take action to prevent crop loss. Using biological control can replace the need for insecticides. Mexican bean beetle (MBB) adults are coppery brown with black spots. They look very much like large ladybeetles and in fact are closely related – but they feed on leaves, not other insects. Adults lay yellow-orange egg masses on the underside of bean leaves. These hatch into bright yellow, spiny oval larvae, which feed, molt several times as they grow, and pupate on the underside of leaves. Feeding damage from adults and larvae can reduce yield and injure pods if numbers are high. There are several generations per season, often increasing in numbers.

The only material for organic growers is Pyganic and its efficacy is at best fair.

Mexican Bean Beetle Larvae.
Pediobius foveolatus is a commercially available biological control agent for Mexican bean beetle control and has a good track record in the mid-Atlantic states and among New England growers who have tried it. (Pediobius is pronounced “pee-dee-OH-bee-us”). It is mass-reared and sold by the New Jersey Dept of Agriculture and is also available from other beneficial insect suppliers. (http://www.state.nj.us/agriculture/divisions/pi/ prog/beneficialinsect.html4).

This small (1-3 mm), non-stinging parasitic wasp lays its eggs in Mexican bean beetle larvae. Wasp larvae feed inside the MBB larva, kill it, and pupate inside it, forming a brownish case or ‘mummy’. About twenty five adult wasps emerge from one mummy. Control continues and in fact gets better as the season progresses and successive generations of the wasp emerge and search out new bean beetle larvae. This makes it well suited to our succession-planted snap bean crops. After a release in the first plants, it is advisable to leave that planting intact for a while, until the new generation of wasps has emerged from their mummies. As with any biological control, make releases as soon as the pest is present – not after it has built up to damaging numbers. The New Jersey Dept of Agriculture Beneficial Insect Rearing Laboratory recommends two releases, two weeks in a row, coinciding with the beginning of Mexican bean beetle egg hatch. Wasps will lay their eggs in larvae of any size, but it is best to target the newly-hatched young MBB larvae. This will give control before damage has been done. Thus, timing is important. Watch for eggs and time the shipment for the first hatch of eggs into larvae. The release rate should be at least 2,000 adult wasps per field for less than an acre, or 3,000 per acre for fields of one acre or more. The 2007 cost from NJDA was $30 plus shipping for 1,000 adults, or $15 for 20 mummies (pupal parasites inside dead MBB larvae) from which about 500 adults will emerge (call for current prices). Order adults if you already have MBB larvae in the field.

Ship for overnight delivery. Instructions for handling and release will come with the wasps. Wasps reproduce in the field and will still be around when the second generation of MBB hatches out. Thus, it should not be necessary to make more than two releases. Like beans, Pediobius wasps are killed by frost. Contact information for New Jersey source: Tom Dorsey, 609-530-4192; address; NJDA, Phillip Alampi Insect Lab, State Police Drive, W. Trenton, NJ 08628. You’ll also get advice on how to use the wasps from this office (website:http://www.state.nj.us/agriculture/divisions/pi/prog/beneficialinsect.html). Pediobius is also available from the following suppliers: Green Spot Ltd., NH., www.greenmethods.com 603-942-8925; IPM Laboratories, NY 315-497-2063; ARBICO, 800 -827-2847 (AZ), http://www.arbico.com/; Network (TN), 615-3704301, http://www.biconet.com/; Rincon Vitova (CA), 800-248-2847, http://www.rinconvitova.com/

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