June 15, 1999
Compiled by Vern Grubinger, University of Vermont Extension
(802) 257-7967 verng@sover.net

Adult Colorado potato beetle observed in Grand Isle and Brandon; no eggs seen yet. Tarnished plant bug at all nymphal and adult stages in Grand Isle, Brandon, Fairfax, Starksboro, and Hinesburg, mostly on strawberries beginning to be seen in other crops. Mites on strawberries in Grand Isle, Brandon, and Fairfax. Cabbage root maggot seen on Brassica crops where no row cover was used in Grand Isle and Fairfax. Adult imported cabbage worm moths have been seen in Fairfax and Grand Isle. Flea beetles have been seen occasionally in Fairfax, Grand Isle, and Brandon. (Pam Adams, IPM scout)

All initial planting complete and rowcovers installed; the usual management sins committed when trying to plant in the middle of bedding plant season and being on the cusp of strawberry season. Weeding and watering the main events ,very dry again. Berries coming along, should be picking a few for farmstands by 6/13 where no rowcovers. After last years meteorological debacle we are trying to be philosophical about what kind of crop is out there? "it aint over 'till it's over." Two-spotted mites showing up in the berry beds, have sprayed once for cuke beetles in vines. Influx of college kids are helping us get caught up. (E. Hartland)

Very dry and windy conditions. Cucumber beetles attacking in huge quantities. Seen a few squash bugs and have a little cabbage root maggot in broccoli. First round of broccoli headed up too early. Field lettuce coming in but could use some steady rain. All melons, squashes, and field tomatoes and peppers are in. (Charlotte)

IPM scout has been a help spotting flea beatles, and TPB, since I had not found time to do it. As a whole, bug pressure seems to be less, I haven't seen much damage from the clipper this year, and only used one spray, prebloom. The berry crop is the earliest I've seen yet, we started picking strawberries for the stand June 5th and will open by June 12th. We still have a lot of bloom in the late berries, so, hopefully it will translate to a long season. We've been irrigating a lot. Greenhouse sales have been very good. (Hinesburg)

First CPB in numbers this past week, finding eggs on potato plants. Weeds pretty well under control so far. Crabgrass was germinating at the end of April beginning of May. Cuke beetles came in fast and furious last week along with some squash bugs, row covers and one spray of rotenone/pyrethrum appears to be working. Major field transplanting done and first CSA harvest this week. Vegetable plant sales about normal, no Y2K rush seen here. (S. Royalton)

Just saw on the Weather Station that La Nina is supposed to make the Northeast wetter than usual this summer. Fire that meteorologist. Cucumber beetles attacking in force, we made a valiant stand at the summer squash. Flea beetles tried a diversionary move on cole crops and radish leaves but were forced them back with a rotenone cloud. Botanigard took out the potato aphids massing on greenhouse tomatoes but made the foliage look like a napalm burn. Mice in the sunflower plugs, crows in the corn. The battle goes on. (Dummerston)

Dry again. Irrigating all fields on most crops except deep rooted ones like potatoes and corn. No rain in sight so we just bring the pipe with us when we plant. First CPB seen last week. No egg masses but plenty of lady bugs. Expecting lots of leafhoppers. Plenty of flea beetles and lots of  damage on greens because we've got to keep row covers off due to the high heat - too much bolting. An entire arugula planting bolted in 23 days after planting! Bird damage on winter squash - lots of seedlings ripped out of the ground. Still, we started harvesting last week and have great lettuce, kale, mizuna, arugula, radish, bok choy, hon tsai tai, and chinese cabbage. Spinach is okay but not growing much in the heat. Peas not flowering much yet. At least the strawberries are primo and we're actually hoping for no rain to give us a nice sweet crop. (Amherst MA)

I have two IPM scouts at the farm this year, although only a few weeks into it I'm struck by the fact that scouting of insects (or diseases) is only part of the IPM process. The mere presence of a pest does not necessarily indicate there is a problem - some pest populations are tolerable and do not cause economic loss, and higher populations can be tolerated at less critical times. For instance, TPB is most critical to control during the bloom period, and cucumber beetles do the most damage to small young plants. Economic thresholds are the level of population for a particular pest in a particular crop at a particular stage of growth at which control makes economic sense. The use of thresholds requires accurate scouting to provide precise population estimates. However without thresholds scouting is just insect observation, and those prone to avoid spraying will say "Oh that's not bad I've seen it worse" and those prone to spray will say "Let's get 'em". I think that the next step for Vermont's vegetable and berry IPM program is the compilation of threshold information. Some individual farmers have this information for whatever crop is their particular passion. If you have you have precise scouting and threshold information at your disposal, dig it out and share it with the rest of us. I'll do the same with my imported cabbage worm information, if I can find it. (Starksboro).

THE ORGANIC STRAWBERRY meeting on June 2 was attended by 30 people. Jake Guest's 3/4 acre field of organic Jewel is in its first fruiting year and looks vigorous, with little insect and disease pressure but moderate weed problems despite keeping it very clean in the planting year. The mulch was thin in the row middles. Among organic berry growers there was consensus that weeds are the primary pest problem overall. Heavier-than-normal mulching seems worth the expense to suppress weeds in organic fields in fruiting years. Few growers reported fruiting more than one year organically, mostly due to weeds. One grower did report years of success using fresh pine sawdust applied a couple months after planting, 1.5 to 2 inches deep around the plants and twice as deep in the row middles. Weekly cultivation precedes the sawdust to assure that fields are kept clean. Then runners set right through the sawdust but the weeds are suppressed for the next 2 fruiting years. Organic growers agreed that Tarnished Plant Bug is their most troublesome insect pest, and that spraying botanical insecticides doesn't work. Floating row covers can limit TPB pressure, and often there is surprisingly good pollination even when covers are taken off after flowering starts. Growers are using row spacings ranging from 36 to 52 inches on center. Several are pleased with drip irrigation as it reduces foliar disease pressure and makes it easy to put on water frequently if needed. How much can you get for organic berries? One grower tries for 30% over conventional, others feel constrained by low conventional prices, especially those near Canada.

BOTANIGUARD-ES WARNING: several reports from MA and VT of edema-like symptoms on greenhouse tomato leaves after spraying Botaniguard mycoinsecticide. Edema is usually caused by a combination of warm soils, high humidity and cool air temps so that the roots keep pumping water up to the tops but transpiration is shut down so cells in the leaves 'explode'. A Mycotech representative told me that it's the oil in the ES formulation that causes the problem, although he suggests that the plants should grow out of it fairly quickly. To avoid the problem they recommend using the wetable powder formulation of Botaniguard that is available at the same price, from the same distributors. Mycotech also recently got EPA approval of an organic formulation that has a vegetable oil instead of a mineral oil carrier, and they will be checking it out for potential to cause edema.

CABBAGE 'WORMS' is the term for caterpillar pests of cabbage, broccoli, cauliflower, kale, etc. that include diamondback moth, imported cabbage worm, and cabbage looper. All of these are leaf-eating green larvae that should be scouted for from June through harvest. Connecticut extension recommends sampling 25 plants per field, then multiply the number of infested plants by 4 to get percent infestation. Stop at ten or more locations per field, randomly selecting 2 or 3 plants per site for close examination of both upper and lower leaf surfaces. You do not have to count the larvae just check for their presence or absence on each plant. Treat cabbage or broccoli with insecticides only if infestation is 20% or more after heading. Cornell recommends the same threshold for the seedling stage of crucifers, increasing to 30% for early vegetative growth that precedes 'heading'. However, Connecticut says that collards or kale should be treated at any time during the season if infestation exceeds 10%. Cauliflower also requires a lower threshold: Cornell says 5% from heading to harvest, Connecticut uses 10% infestation.

FLEA BEETLES can be especially damaging to seedings so thresholds for insecticide application are based on plant size. Cornell suggests treatment if there are 2 beetles per plant when eggplant is 3 inches or shorter, 4 beetles per plant when plants are 3 to 6 inches tall, and 8 beetles per plant when plants are taller than 6 inches. Rutgers thresholds are the same, and they suggest scouting weekly, paying particular attention to field edges or weedy areas. Try to avoid casting a shadow on plants to be sampled, count beetles as you approach the plant.

CUCUMBER BEETLES are out in force, and are of special concern when cucurbit plants are small. UMass and Cornell suggests scouting twice a week, especially when plants have less than 5 leaves. Inspect 25 plants, walking a V-shaped pattern ans selecting plants without bias. Examine undersides of cotyledons, young leaves and stems. Thresholds for insecticide vary depending on crop susceptibility to bacterial wilt, which is spread by the beetles. Squash, pumpkin and watermelon are not highly susceptible, and they can withstand significant defoliation. Early in the season, when plants 5 leaves or less, the threshold is 5 or more beetles per plant on pumpkin or watermelon, 2 or more beetles per plant on summer or winter squash. Cucumber and cantaloupe are highly susceptible to bacterial wilt. If plants along field edges are heavily damaged, or there is just 1 beetle per 100 foot of row, treatment may be warranted to avoid the spread of bacterial wilt. After plants of all species have more than 5 leaves scouting should continue and treatment applied if blossoms are heavily infested and being damaged during peak bloom, or young fruit are being fed upon.

2-SPOTTED SPIDER MITES IN STRAWBERRIES are being found across the region, encouraged by the warm dry weather. According to University of Maine Strawberry IPM newsletter it is important to scout for them regularly because plants can become weakened and stunted from their feeding on leaf undersides, where they rasp tissue and suck sap. Infested leaves develop yellow flecking and bronzed appearance. Fields with rowcovers and/or excessive nitrogen fertility seem to be the most susceptible to injury. To scout, collect 60 leaves from throughout the field and examine for presence or absence of mites. Be sure to use a hand lens to help you see them. If 25% of leaves are infested (15 or more leaves) treatment is suggested. Note that certain pesticides such as carbaryl, chlorpyrifos, difocol and benlate are harmful to the natural enemies of spider mites, and should be avoided if possible. A native spider mite predator, Amblyseius fallacis, is commercially available from several companies.