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 MOFGA's 2011 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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MOFGA's Pest Report - July 8, 2011
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Late Blight:
At this time there are no active reports of late blight closer than Long Island, New York. I will send out an “UPDATE” if things change, and an “ALERT” if it, or something else very serious, gets to be an immediate threat. If you are not already on my Pest Report Email List, send me an email and I'll add you to the list.

Squash Vine Borer: (Adapted from an article in the U Mass Vegetable Notes). Squash vine borers are showing up in traps in NH at their highest level in 5 years, and squash bugs (see below) have been seen colonizing cucurbit crops. Many vine crops are in bloom, and care should be taken during bloom to avoid insecticides which are toxic to pollinators, e.g., pyrethrum.

Squash vine borer moths are day-flying moths with a 1.0 to 1.5 inch wingspan and bright orange markings. In flight, they look like wasps. There is one generation each year and adults emerge in late June/early July. They lay eggs at the base of squash plants, and upon hatching, larvae bore into stems (where they are protected from insecticides). Thick-stemmed squashes are preferred. Unless you use traps or scout fields for evidence of eggs or larvae, the first sign of squash vine borer infestation is often wilting vines in July and August. By that time, it is too late to do anything.

Growers should scout their pumpkin and squash fields weekly for squash vine borer from late June through early August. Examine the base of vines for evidence of larval feeding (sawdust-like frass near entrance holes) and then split open the stem to confirm the presence of larvae, which suggests more eggs are being laid. Two insecticide sprays, ideally applied to the base of the plants and timed five to seven days apart, will control newly hatching larvae before they are able to bore into the stem. Treat base of stems thoroughly to target hatching larvae. Spinosad (Entrust) provides excellent control of hatching SVB larvae if you catch them before they bore into the stem.

Alternatively, you can monitor with a Scentry Heliothis pheromone trap from early June through early August. Make 2 to 4 weekly applications if more than 5 moths per week are captured. Timing is very important. - Source material from New England Vegetable Management Guide; Handbook of Vegetable Pests, A Capinera; ATTRA.
Adapted by Andy Cavanagh & R Hazzard, UMass Extension.

Squash Bug: (Adapted from an article in the U Mass Vegetable Notes). Squash bugs (Anasis tristis) are serious pests of pumpkins and squash throughout North America. Damage and survival are low on watermelon, very low on cucumber and muskmelon, and highest on squash and pumpkin. Both adults and nymphs feed by inserting their beak and sucking juices from plant tissue. Toxic saliva injected during feeding causes foliage to wilt, then turn black and die; the severity of this damage is directly related to density of squash bugs on each plant. Later in the season, squash bugs may feed on the fruit, causing them to collapse or become unmarketable.

Adults are 0.5 to 0.75 of an inch long, flattened and grayish-brown. They hibernate in trash in and around the garden for the winter and emerge in the early summer to feed a bit and lay eggs. Eggs are laid in clusters usually on the underside of leaves and are orange when first laid, but turn bronze-colored before they hatch. The wingless nymphs are similar in appearance to adults, and are whitish when small, with a brown head, and grayish white when larger with black legs. There is one generation per year in the Northeast.

Black plastic, straw mulch, and reduced tillage systems encourage higher populations, probably by providing good hiding places.

Squash bug numbers are reduced by clean cultivation in the fall, and crop rotation. Infestation is delayed by row covers. If possible, rotate cucurbit crops between fields as far apart as possible. Keep headlands mowed and free of trash to reduce overwintering sites.

Squash bugs are unusually difficult to control with insecticides. Scout undersides of leaves for squash bug adults and eggs. Crush the eggs, but you may not want to crush the bugs as they stink when you do. Treat if the copper-colored egg masses exceed one per plant. Time squash bug sprays to kill young nymphs just after hatch, because this stage is the easiest to control. Treat late in the day when the flowers are closed to reduce risk to bees. Neem products have proved effective.

For adult bug control, insecticides applied to the base of the plant are most effective, possibly because bugs tend to cluster. But, squash bugs are virtually impossible to control later in the season when nymphs are large and the canopy is dense. - Source material from New England Vegetable Management Guide; Handbook of Vegetable Pests, A Capinera; ATTRA. Adapted by Andy Cavanagh & R Hazzard, UMass Extension.

Squash bug adult and eggs.

Squash bug young nymphs and eggs.

Squash bug older nymphs.

Photos by Eric Sideman.

Caterpillars In Brassica Crops: There are three common caterpillars that feed on our broccoli family crops. Keep an eye out for them. The imported cabbageworm butterflies are flying now.

Quick ID Cues
  • Diamondback moth caterpillar: Green, very wiggly when poked, pointed on both ends, not fuzzy, only grows to about 1/2 inch. You may find white silken cocoons. They eat wholes in the leaves. There are many generations in a single season, even though they do not overwinter here.
  • Imported cabbageworm: gray-green, slightly fuzzy, and sluggish. Grows to >1 inch and favors the center of the head as it gets larger. Leaves wet green frass (droppings). Eggs single, light green or yellow. They eat large chunks out of leaves. The adults are those white butterflies you commonly see flying around your broccoli.
  • Cabbage looper: light green, smooth, loops up like an inch worm as it moves. Eats big holes in leaves. Scout undersides of leaves to look for fresh damage, and get control of the caterpillars when they are small and damage is slight. Check heading crops as soon as heads start to form. Greens should be scouted at all growth stages.
For organic growers both Bt and Spinosad are very effective (Bt products are a lot cheaper), but remember to only spray after scouting and assessing damage. The pest has to be there to be killed, i.e., neither material has long efficacy after spraying. Destroy crop after harvest so it does not act as a harbor for the pests all season.

Diamondback larvae

Imported cabbage worm.

Photos by Eric Sideman.

Rose Chafer:
The rose chafer is in the same family of beetles as the Japanese beetle and has a similar life history.

The adult is out now and voraciously feeding on many different crops such as rose, raspberries, apples, grapes and some vegetables too. They skeletonize the leaves and are feeding on blossoms and young fruit too.

The adult is a half inch long, gray-tan beetle with a reddish-brown head. The adults are mating now and will lay white, shiny eggs in the soil soon. The larvae are white grubs that live in sod feeding on roots, especially on sandy ground. The life span of the adult is only about three weeks so you may just want to wait them out. But if your population is large you may loose your crop while you wait.

Crop rotation will not help because they are good fliers. You may be able to control grubs with beneficial nematodes, but that is likely to help little with controlling adults because your neighbor's sod ground will be a source even if yours is not. Hand picking or knocking the critter off the leaf into a jar of water works well for small plantings. Pyganic and Surround seem to do little to deter adults. Rotenone may work, but there are no formulations permitted in organic production and its EPA registration as an insecticide has been dropped. I have heard from a grower that neem oil works well, especially a neem and diatomaceous earth combo. Has anyone else tried that with success? Are there any other suggestions?

Leafhoppers: (repeated from June 23 issue because this is important). 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.

Measuring Insecticides For Backpack Sprayers And Small Plantings: (Modified, short version of an article by Ruth Hazzard in the Umass. Veg. Newsletter. For the complete article with examples go to http://www.umassvegetable.org/newsletters/current_news.html and look at the June 17, 2010 issue)

Growers with diverse crops and small plantings often need to be able to apply pesticide to beds or plots of several hundred square feet rather than acres, and the pesticide labels often only give rates on per acre basis. It is important to use the correct amount of insecticide in your backpack sprayer when spraying a small area. Calibration and mixing require some basic math, as do a lot of aspects of farming! The methods for backpack sprayers and tractor sprayers are essentially the same. Figure out the area to be sprayed and how much pesticide is needed for that area. Measure the amount of water you need to cover a known area, using the same equipment and walking or driving speed that you will use when spraying. Then ‘do the math’ so that the insecticide and the water rates both match your target area. Why does it matter? Why do you need to be careful about these rates? 1. Effective control of the pest depends on correct rates. 2. You are legally responsible for following the label instructions. This is especially important when you are selling the crop to the public. 3. The safety of the applicator, workers and the public depends upon correct rates and using pesticides according to instructions on the label.

Read the label. Find and follow the following instructions: --Personal protective equipment (PPE) – what you must wear when mixing and spraying. --Agricultural Use Requirements – this tells what protective equipment you should wear. --Crops and pests listed. The pesticide MUST be labeled for the target crop. --Restricted Entry Interval (REI) – during this time, no one should work in the sprayed area unless they are wearing protective equipment. --Days to Harvest (DH) – how long you must wait after a spray before harvesting (note: days to harvest may be less than REI; it is not a misprint) --Rate per acre or concentration per gallon (for backpack sprayer) --Mixing instructions.

The label often uses inconvenient measures. Conversions are key to your calculations. Here are some conversion ratios: 16 dry oz (by wt) = 1 lb One ounce (dry weight) equals 28.45 grams. 32 fl oz = 1 qt. 128 fl oz = 1 gal Liquid measure in (fluid) ounces is already a volume so it is easier to measure. One fluid ounce equals 6 teaspoons (tsp) or 29.6 milliliters (ml). An inexpensive measuring device for ml can be found in the children’s medicine section of drug stores. 43560 sq ft = 1 acre. Entrust, for example- Based on repeated samples, we have found that there is 1.7 gm per teaspoon (shaved level and tamped slightly). So for Entrust the recommendation is 1.3 grams (3/4 teaspoon) in 3 gallons of water for 1,000 sq. ft.

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