2001 SWEET CORN HERBICIDE UPDATE
by Dr. Rich Bonanno, UMass Extension

Because sweet corn has several highly effective registered herbicide options, vegetable growers can take the opportunity to reduce weed pressure by rotating their fields to sweet corn occasionally and maximizing control during the sweet corn year. Many growers combine timely cultivations with herbicides. Remember to always keep cultivations shallow, cultivate when weeds are small, and orient the rows to minimize soil erosion during times of heavy rainfall.

Over the past year, there have been new herbicide registrations and label changes for weed management in sweet corn. This article covers the basics. Please check both the herbicide labels as well as the current New England Vegetable Management Guide for additional information (most of these changes will not appear until the 2002-2003 version of the guide is published late in 2001). Remember that the label is the final authority. As with all new pesticide registrations, growers should gain experience with these products before using them on a wide scale.

New Registrations.
Permit (halosulfuron) 75% WSG, 2/3 to 1.33 oz. per acre (0.032 to 0.063 lb active ingredient (a.i.) per acre). This herbicide provides postemergence control of many weed species which are not under drought stress. It is rainfast in 4 hours. Use a non-ionic surfactant at a rate of 1 to 2 qt. per 100 gal spray or a  crop oil concentrate at 1 gal. per 100 gal. spray. Control varies with type and size of weed. Species listed on the label include redroot pigweed, pokeweed, common ragweed, Pennsylvania smartweed, common sunflower, velvetleaf, wild mustard, yellow nutsedge, and wild radish. Do not cultivate for 7 days after application. Most vegetables can be planted within 12 months of application except crucifers, carrot, leeks, onions, lettuce, beets, and spinach. Some sweet corn varieties may be injured by Permit and no reliable list of susceptible varieties has yet been  developed. Regular sugary varieties do not appear to be more tolerant than se (sugar enhanced) types or sh2 (supersweet) types. Initially, this herbicide should be used on a small scale to control problem weeds such as yellow nutsedge, ragweed, velvetleaf, and triazine-resistant lambsquarters. Other postemergence options continue to exist. These include AAtrex (atrazine), Basagran (bentazon), Formula 40 (2,4-D), Lorox (linuron), and Evik (ametryn).  Atrazine, Basagran, and 2,4-D have been the most commonly used.

Prowl (pendimethalin) 3.3 EC, 1.8 to 4.8 pt. per acre (0.75 to 1.9 lb a.i. per acre). Apply preemergence only after seeding. DO NOT incorporate into the soil. A broadleaf herbicide such as atrazine, Bladex, or simazine should also be used to control broadleaf weeds. If this herbicide is moved into the seed zone, there is potential for crop injury. Some basic suggestions for minimizing the potential for crop injury are to plant in a firm seedbed, plant corn seed at least 1.5 inches deep, plant into moisture rather than into dry soil, do no mix Prowl with liquid fertilizers, and avoid sandy soils. If the soil is dry, consider irrigating of waiting for rainfall prior to application.  If heavy rains follow an application to dry soil, Prowl can move to the seed zone and cause crop injury. Specific weeds for which this herbicide should be considered include triazine-resistant lambsquarters, and velvetleaf. Growers may consider a lower rate of Prowl in addition to using a broadleaf herbicide and another grass herbicide such as Dual Magnum, Lasso, Frontier, or Eradicane.

Frontier (dimethenamid) 6 EC, 16 to 32 oz. per acre (0.75 to 1 lb per acre). Apply to preplant surface, pre-emergence or post-emergence (corn can be up to 18 inches tall). A split application can be used. Frontier will not control emerged weeds. A broadleaf herbicide such as atrazine, Bladex, or simazine should also be used to control broadleaf weeds. Some sweet corn varieties may be injured by Frontier and no reliable list of susceptible varieties has yet been developed. Frontier has activity which is similar to Dual Magnum and Lasso. It offers an alternative for rotational purposes. Growers should gain some experience before widespread use on the farm.

Modified Registrations.
Bladex (cyanazine) 4L, 1 qt. per acre (1 lb a.i. per acre) is new maximum rate. Apply after seeding but before crop emergence. Bladex is weak on most grasses but excellent on many broadleaf species. The last year for use is 2002. Observe all label precautions related to tractor cabs and applicator safety.

CyPro (atrazine + cyanazine) DF. This is a formulated prepack of Atrazine and Bladex (cyanazine). This cannot be used postemergence in sweet corn because of the Bladex which can seriously injure of kill emerged sweet corn. It should be used in combination with a grass herbicide such as Dual Magnum, Lasso, Prowl, Eradicane, or Frontier. The use rate for this product for 2001 and 2002 is 1.5 lb/acre (1 lb a.i. per acre cyanazine and 0.32 lb a.i. per acre atrazine).  Depending on weed pressure, additional atrazine at planting, cultivation, or a postemergence application of atrazine, Basagran, 2,4-D, Permit, Lorox, or Evik may be needed.

Dual Magnum and Dual II Magnum (metolachlor) 7.6 EC., 13 to 27 oz. per acre (0.77 to 1.6 lb a.i. per acre). Can be applied at planting or up to 5 inch tall corn. Apply to weed free soil. Dual Magnum has excellent activity on grasses and is weak on lambsquarters. These formulations replace Dual and Dual II. The "II" is a safener which may lessen the potential for crop injury in cold soils. Basically, the activity of the Magnum formulation is the same as with the old Dual but the use rates are lower. When these products occur in prepacks with atrazine, they are called Bicep and Bicep II.

(Mention of pesticide brand names is for information purposes only, no endorsement or discrimination is intended. Always follow the label.)

SMALL SCALE FRUIT PRODUCTION: A COMPREHENSIVE ON-LINE GUIDE
(located at http://ssfruit.cas.psu.edu/ ). Created by Penn State Univ., this guide discusses topics such as getting started, pruning and training fruit trees, pests and pesticides, and controlling wildlife damage. It also includes individual chapters for each fruit type (pome, stone, grapes, berries, kiwi, etc.). Each of these includes fruit-specific information on planting, nutrition, harvest, and pest management, among other topics. This is a well-organized and very handy resource for anyone planning or maintaining a fruit garden. (submitted by Howard Cheshire).

MARIGOLDS AS GREENHOUSE INDICATOR PLANTS
(By David Cappaert, Dept. Entomology, Michigan State Univ. via greengrower@list.uvm.edu)

During this past winter/spring, I assisted on a small greenhouse production project. The crop was 2000 sq. ft. of edible flowers, a broad mix of pot plants--nasturtium, sages, viola, daylily, basil, mints, parsley, etc. My mission was biocontrol of the pests, as pesticides were not acceptable.
We monitored insects weekly in two ways: 1) Sticky-card count, from two cards per house, cards suspended 1 meter above bench surfaces. Our intent was to sample from the general background
of pests, avoiding "contamination" of a card more closely associated with a single planting.
2) Indicator plant counts, observing the insects shaken onto a white sheet of paper from 2 flowering marigolds/bench of 60 sq. ft.

The indicator plant method probably involved a little more effort, but was dramatically more useful in guiding pest control decisions. The marigolds detected 4 pest (thrips, whitefly, spidermite, aphid) and 4 natural enemy (predatory mites, Orius, lacewing, Aphidius) species. Sensitivity to thrips was particularly good, probably adequate to guide management decisions. In
fact, based on the virtual absence of thrips in the sticky-card catch, and lack of thrips damage, we were generally observing a population level beneath the notice of most growers. But this measure of low thrips levels is key to timely use of biocontrols. Marigolds were also good
indicators for aphids, which appeared on the indicator in the same week in which crop plants were infested (as seen in weekly scouting). Marigold counts of whitefly and spidermite were less reliable--direct scouting of local infestation was necessary for these.

On the other hand, the sticky cards really only measured fungus gnat numbers. I'll argue that in many situations, this data is not very important--FG's are not especially threatening in most crops, and nuisance levels are quite evident enough without a specific card count. Thrips were absent in most weeks, while the marigolds indicated a steadily rising number.

So in many growing situations, where early detection of thrips and aphids is critical, the indicator plant is probably the way to go. A second advantage in a biocontrol context is that these flowering indicators will also provide refuge and pollen for natural enemies.