Several herbicides are registered for use in vegetable crops as burndown products in stale and false seedbed systems. False seedbeds are prepared well in advance of vegetable seeding, and weed seedlings are encouraged to emerge before the crop is seeded. Cultivation, herbicide application, or flaming are used to destroy the emerged seedlings.
Stale seedbeds sometimes are used for vegetable production when other selective weed control practices are limited or unavailable. The soil is tilled, vegetables are planted and weed seedlings are killed using herbicides, flames, or blind tillage before the crop emerges. Use of tillage is only possible with large seeded vegetable crops that are planted far enough below the soil that precision tillage implements can avoid contact with the crop seed. Success of these systems depends on controlling the first flush of emerged weeds before crop emergence, and on minimal soil disturbance, which reduces subsequent weed flushes while the crop establishes. After establishment, other weed control practices including cultivation or other herbicides can be used. Stale seedbed steps are:
Prepare a seedbed, preferably 2 to 3 weeks before planting, to achieve maximum weed seed germination near the soil surface. Soil temperatures and moisture must be reasonable, or results will be erratic.
Plant the crop with minimum soil disturbance to avoid exposing new weed seed to favorable germinating conditions.
After planting (depending on herbicide or strategy), but before crop emerges, treat the field by flaming or with herbicide to kill all germinated or exposed weeds.
carfentrazone (Aim EC)
Rate Up to 0.031 lb ai/a (2 fl oz Aim EC)
Time Preplant interval varies by crop. See PREPLANT BURNDOWN section of the product label for instructions.
Remarks The use of a nonionic surfactant, crop oil concentrate, or methylated seed oil is required. A high-quality sprayable liquid nitrogen fertilizer may be used at 2% to 4% v/v or AMS at 2 to 4 lb/a in addition to the nonionic surfactant, COC, or MSO. Tank mixes with other herbicides increase spectrum of control. Apply to actively growing weeds not more than 4 inches tall, or rosettes 3 inches in diameter. Thorough coverage is essential for good control.
Caution Do not apply to desirable vegetation.
Site of action Group 14: protoporphyrinogen oxidase inhibitor
Chemical family Triazolinone
Use liquid propane or similar fuel-burning equipment to quickly sear weeds. Use the thumb pressure test to determine effectiveness: press a weed leaf between thumb and forefinger; if the leaf collapses and a thumb print remains, sufficient heat was applied to kill the leaves. There may be no other noticeable change in the plant immediately after flame is applied. The objective is to disrupt cell membranes, not to char the plant.
Rate 0.5 to 2 lb ae/a
Time Apply to seedbeds before or shortly after the crop is planted, but before the crop emerges.
Remarks Refer to the table "Registered Uses of Glyphosate" in this chapter for general guidelines; read the label carefully to determine proper timing and which product can be applied to each crop.
Caution Some crops may be injured by glyphosate if the soil is extremely sandy, or if the planter did not properly close the seed row. Do not allow glyphosate to contact seeds or any part of the seedling, as crop failure will result.
Site of action Group 9: inhibits EPSP synthase
Chemical family None generally accepted
paraquat (Gramoxone Max) or diquat (Reglone)
Rate Consult label
Time Apply during or after planting but before crop emerges.
Remarks Use paraquat if grasses are present. Add a nonionic surfactant or crop oil concentrate according to label specifications; take care to avoid anionic formulations that react in the tank to form insoluble precipitates. Exposed crop plants will be killed. Acts as contact; absorbs energy produced by photosynthesis, forming peroxides that disrupt living cells.
Caution Paraquat is a restricted-use herbicide. Do not ingest or inhale spray mist. Wearing protective face shields, respirators, and clothing is advised. Do not apply preplant or preemergence to soils lacking clay minerals, such as peat, muck, pure sand, or artificial planting media. Paraquat can be used in these crops (not an exhaustive list): beans, lima and snap; broccoli; cabbage; cabbage, Chinese; cantaloupe; carrots; cauliflower; collards; corn, sweet; cucumber; eggplant; garlic; lettuce; melons, musk; onions, green and dry bulb; peas; peppers; squash; tomatoes; turnips; watermelon.
Site of action (both) Group 22: photosystem I electron diversion
Chemical family (both) Bipyridilium