Growers have little influence on the weather beyond prayer, but they can prevent the devastating crop losses that occur when vegetables are planted in fields containing residues of persistent herbicides. Even though herbicides used on vegetables may persist and injure a subsequent crop, most problems occur when vegetables follow corn or other agronomic crops that were treated with a soil-active product.

Remembering and following a few simple guidelines will usually prevent problems.

Rule number one is to read the label. Product labels are required to state how long you must wait following application before planting rotational crops. Planting a rotational crop sooner than the interval stipulated on the label is a recipe for disaster. Read the label.

Purchasing or renting new land? Don’t plant until you know which herbicides were used in previous years, when they were applied, and what rates were used. The further back you go, the better! Remember, replant schedules may not be available for every vegetable. A bioassay may help estimate the risk of carryover, when label information is unavailable. Directions on conducting bioassays can be found in Ohio State University’s (OSU) Extension Vegetable Production Guide (Bulletin 672).

Previous-year growing conditions directly affect how long herbicide residues persist. Cool, dry summers and early winter conditions can reduce herbicide breakdown, greatly increasing the chance that carryover will be a problem next spring. Under these conditions, a bioassay is a good idea before planting, even if the label indicates enough time has elapsed to safely plant vegetables.

In 1999, experiments were started to determine tolerance of tomato, cabbage, potato, bell peppers, and snap bean to Hornet soil residues. Also, potato, sweet corn, and oats were rated for sensitivity to soil residues of Firstrate. Research was conducted at the Vegetable Crops Branch of OARDC near Fremont, Ohio.

The soil had a pH of 5.5 and 3% organic matter. Hornet was applied postemergence (POST) on corn at 0, 2.4, 4.8, and 9.6 oz/a, and Stinger a 8 oz/a. Northstar and Accent were applied at 10 and 0.7 oz/a, respectively. Firstrate on soybeans was applied PRE at 0, 0.8, 1.5, and 3 oz/a and POST at 0, 0.6, 1.2, and 2.4 oz/a. Pursuit and Classic were applied POST at 2.9 and 0.8 oz/a. POST treatments were applied when the corn was at 5 to 6 collars, and soybeans at 5 to 6 trifoliates. In 2000, the vegetable crops were planted across the plots, and no additional herbicides were used. Vegetable crops were evaluated for injury at 7, 14, 28, and 42 days after emergence (DAE) or days after transplanting (DAT).

Cabbage was highly sensitive to Hornet, with symptoms visible 7 DAE; 33 DAE injury was severe in plots previously treated with 4.8 and 9.6 oz/a. Potatoes were also highly sensitive to Hornet carryover. Potato plants were thinned in plots previously treated with Hornet at 2.4 oz/a. At 4.8 oz/a, 50 percent crop injury was observed.

In summary, potatoes were most sensitive to Pursuit, followed closely by their sensitivity to Classic and Firstrate. Sweet corn was very sensitive to Pursuit and the higher rates of Firstrate, even though symptoms took more time to develop. Cabbage, potatoes, snap beans, bell peppers, and tomatoes should not be included in rotations following crops treated with either Hornet, Stinger, or Accent. Of all the products evaluated, Northstar carryover caused the least damage to rotational vegetables.