Procedures After Herbicide Application
by Dr. C.C. Powell

1. Keeping Application Records. Every time a pesticide of any type is applied, a complete record of the application should be made. Pesticide records will be the basis for any changes that may be needed in the pest control program in the future.

2. Cultivating After Treating With An Herbicide. Soil treated with most preemergence herbicides can be cultivated to a depth of 1.5 inches without reducing weed control. Some products form a chemical barrier on the soil surface that burns off weed seedlings as they emerge. They need light to be active. Anything that breaks that soil barrier or covers the herbicide layer will reduce their effectiveness. Check the labels for these types of products.

3. Use application equipment only for herbicides for these tasks and keep them very clean.

4. Controlling Plant Damage From Herbicide Residues. If herbicides have been used properly, damage from residues should not be a problem. If you suspect a misapplication or if weather conditions were not optimum at the time of the application, you may want to conduct a biological test (a bioassay) with sensitive plants to see if they grow normally.

Plant the seeds of herbicide-sensitive plants in liner pots filled with soil from the test site and in other liner pots with soil from a site where no herbicides were applied. Sensitive broadleaf plants are radishes, tomatoes, lettuce, and beans. Sensitive grasses are oats and annual ryegrass. Grow the plants for 2 to 3 weeks and observe for normal development.

5. Planting To Protect Plants From Herbicide Residues. If planting in soil where injury from herbicide residues is a possibility, dip the moist roots of the transplants into dry activated carbon or into a slurry of 1 pound activated carbon per gallon of water before transplanting them.

If you want to treat the soil before transplanting, activated carbon may be spread on the field to neutralize the herbicide. From 100 to 200 pounds of activated carbon per acre should detoxify normal herbicide residues. You can apply the carbon in a band, rather than broadcast, so that only 1/4 to 1/3 of the amounts is needed.

If dry-powdered charcoal is used, spread it evenly over the affected areas. Incorporate the charcoal 4 to 6 inches deep, with a rototiller. Water the area thoroughly every day for 3 to 4 days before planting. If possible, wait a few more days because, under cool soil conditions, deactivation is slowed.