August 1, 2000
Compiled by Vern Grubinger, University of Vermont Extension
(802) 257-7967

(Starksboro) I discovered a dramatic discrepancy in the action thresholds for potato leaf hoppers (PLH). I've been using the book "Diseases and Pests of Vegetable Crops in Canada" as my bible for pest control. It has excellent pictures along with very thorough information about damage, life history, management, cultural practices, biological controls and chemical control for all the insects and diseases imaginable. This year I have also started getting the UMass IPM newsletter by E-mail. The two sources recommend very different action thresholds for PLH. The Canadian book says 10 nymphs per 100 mid-level leaves. UMass says 10  nymphs OR adults per 100 mid level leaves. Big difference. Here I was patiently waiting (10 days or more) for the nymphs to hatch out, while the field was full of adults feeding and injecting their poison into the plants. The crop is OK by and large, but there are sections of the field where the plants are stunted and show leaf edge symptoms of hopper damage. Another lesson learned.

A very wet week just following the middle of July advanced the spray requirements for tomato fungicide very rapidly according to the TomCast model. Field tomatoes are running late this year, and quite frankly a little early blight might hasten ripening. I'm hoping for the first tomatoes 10 days later than average, and the first corn equally late. Everything else, however, is maturing at average dates. Prices at the wholesale level seem high for many items including lettuce, squash, and red potatoes. First spraying for imported cabbage worms the last week in July, which is late. I'm keeping an eye open for fall army worms, but have seen nothing yet.

(Charlotte) Things going well. Cool nights make it hard for the tomatoes to ripen. Beautiful potatoes this year. Not a sign of leafhoppers and few CPBs. All in full flower and not planning to spray. Summer squash would love some hot weather but doing quite well. Corn won't happen this year and probably never again. I hate to water it. Lots of peppers in the greenhouse and tomatoes starting to ripen more. Sunflowers seem to be short and flowering early. Otherwise, a happy farm.

(Marlboro) GREAT crop on the blueberries- the best ever! Wet spring means quite a bit of root disease in raspberries. Summer might finally almost be here.

(Wilmington) I have just read all vegetable and berry news E-mails from April, 2000. Love them. Sorry we missed the July meeting but keep us posted. Our son will be attending agricultural college in the fall, I am sure he will learn wonderful things and come home and take over! In
response to the earlier discussion on farm income, we always paid him to work and made him invest $2000 in a Roth IRA before we let him even buy a car. That modest investment at 16 should net him $365,000.00 at 65 even at a modest rate of growth! Farmers need to plan for retirement (ha-ha) as early as possible! The flowers look great so do the weeds unfortunately! Plant sales are great, we are now looking forward to PYO Blueberries. We were able to get the regulations in town changed to allow off-site signage for agricultural endeavors!

(Argyle, NY) Cucumber beetles are at their worst and cool temperatures are keeping vine crops growing slowly.  Overall, most crops doing well, especially ones that like cool weather.   We're still picking peas!!  Received 3" of rain last weekend which drowned all the spinach.  This past Saturday was the first day people swarmed the farmers markets, so sales are good.  What will Mother Nature bring us next?

(Amherst, MA) Drying out here this week. Finally. Crops are growing despite some temps in the low 40s over the weekend. Squash and cukes have finally started producing, the lettuce is as good as we've ever seen, scallions, radicchio, beans, and carrots all look very nice. Incredible leafhopper damage this year - all potatoes dying or dead by now - should be a record-low yield. Corn is all weed free (finally) and growing well despite lots of crow damage. Winter squash is doing well in the field as are leeks, melons, and fall brassicas. Flea beetle pressure very intense still on eggplant. Generally, though the farm is pretty weed free and growing well - we have started the big harvests.

SWEET CORN PEST UPDATE (adapted from Cornell and UMass Extension)
Low numbers of Corn Ear Worm (CEW) are being caught in the Hudson Valley and Capital District of New York. In Massachusetts, CEW numbers are heaviest near the coast and in the Southeast, calling for a four-day spray schedule on silk. Moths have also made their way into the Berkshires and up the Connecticut River Valley in numbers that call for a 5 day spray schedule. CEW is the most serious insect pest on sweet corn because it lays it's eggs directly on the silk. CEW is migratory and comes up on storms from the south. It used to be CEW arrived later in the season but the for last 3 years CEW has been caught in July. For conventional growers, Warrior is probably the best product to be used against CEW. Organic growers can use the Zea-Later oil applicator to protect corn in silk from CEW by putting a few drops of vegetable oil mixed with Bt directly into the silk channel. It's probably too late to get one of these custom-made hand applicators for use this year, but let me know if you're interested in using one next season.

This year, an unusual type of rust for the northeast, southern corn rust is being reported on corn in Michigan and New York. It could reduce yields and affect sales of sweet corn by damaging the appearance of husks. Development and spread of common rust is favored by cool temperatures (61-73  degrees F) and high relative humidity (100%). Rust pustules are usually most abundant on the leaves, occurring simultaneously on both leaf surfaces. They are light-brown and become dark brown as the plant matures. If leaves become covered with pustules, chlorosis and death may occur. Scouting should begin as soon as pustules are detected. Sample 120 plants per field. Record the number of leaves with any rust pustules and count the number of leaves on each plant. Spray when 80 % of the leaves are infected. Once you reach the threshold, spray the plants every 7-10 days. It is important to try and keep rust from infecting ears of fresh market sweet corn because it may make the corn unmarketable. For best results, fungicide applications should be made prior to tassel. Fungicides recommended for control of rust include: Maneb, Manex, Dithane NT, Tilt, and Bravo Ultrex. Tilt and Bravo have a 14-day harvest interval and others have a 7-day harvest interval. This threshold is not valid for highly susceptible varieties.

COLE CROP DISEASE REMINDER (from Brian Caldwell, Cornell Extension)
Downy mildew and Alternaria are two diseases that should be scouted for on cole crops during moist weather. Symptoms of downy mildew are small, irregularly shaped grayish-purple spots on stems and undersides of leaves. During cool, moist conditions the spots enlarge and a fluffy, grayish-white fungus develops. Symptoms for Alternaria are circular, small, dark spots on the upper surface of older leaves. These spots are usually covered with a brown or black velvety mold. The brown or black spores of this fungus can easily be rubbed off the spots they are covering. If your cole crops are on at least a three-year rotation, these diseases may not be a problem. Once they get established in a field, a spray program may be necessary to prevent spread of the disease. Both diseases may be kept in check with a timely application of copper materials.

LOW PSNT NUMBERS (from Bill Jokela, UVM)
We've seen quite a few low Pre-Sidedress Nitrate test (PSNT) numbers coming through the lab this year. A big factor this spring may be the heavy rain and cool temperatures we've had. This means slower mineralization of N from organic material and, perhaps, greater losses (leaching, denitrification) of nitrate that is released. We have noted that the PSNT often does not reflect the full crop N value of a plow-down sod (previous legume-grass hay, but the same principle would apply for legume cover crop such as hairy vetch). Apparently N release is slow enough that the PSNT is taken a little too early to measure the available N as nitrate. We have tried to account for this phenomenon in our PSNT recommendations for field corn by reducing the N fertilizer recommendation by 30 lb/acre when a well-managed sod had been plowed down. The 30 lb/acre adjustment is a rough estimate and certainly varies with weather, nature of the plowed down material, etc. It is not uncommon for a plow-down of winter rye, especially as it becomes more mature, to actually cause a temporary depletion of soil nitrate via immobilization or, at least, to not mineralize much nitrate early in the season. Eventually, N will be released from plowed-down cover crops but it may or may not be in sync with the crop N needs.

Leaf analysis (also called tissue analysis) is an excellent means of monitoring plant nutrient levels. With perennial fruit crops, leaf analysis is even better than soil tests for determining an optimal fertilization program. While soil tests reveal the quantity of  nutrients in the soil, leaf analysis shows exactly what the plant has succeeded in taking up. However, soil tests are necessary for determining soil pH and thus lime (or sulfur) recommendations. If nutritional problems are suspected in a given planting, it's a good idea to take both leaf and soil tests.

Leaf analysis helps detect nutrient deficiencies (especially of minor nutrients) before they effect plant health or yield. For a good tissue test, select green, healthy, whole leaves. Do not submit leaves with disease, leaf burn, insect or hail damage. Keep the leaves in a cool place (insulated chest) or refrigerate before mailing. Record all foliar sprays since the results can be influenced by nutrient or pesticide applications.

A minimum of 50 leaves from raspberries or strawberries, and 80 to 100 leaves from blueberries  should be selected for each analysis. Do not mix leaves from fields with different soil types or management histories. Do not combine leaves from healthy plants with plants that are not growing well. Strawberry samples should be taken from the first fully-expanded leaves after renovation, about July 15 to August 15. Raspberry samples should be leaves from non-fruiting canes taken between August 1 and 20. Blueberry samples should be leaves taken during the first week of harvest, from July 15 to August 15.

Place samples in sealed paper bags, clearly labeled with field names. Include a check for $20 per sample, made out to UVM Ag Testing Lab, with the sample(s). Mail to: Ag Testing Lab, Hills Building, Burlington VT 05405-0082, or deliver the sample in person during working hours. The Lab is on the third floor of Hills Building, just west of the water tower on the UVM campus. Call 1-800-244-6402 for more information.