Application Reminders for Roundup Brand Agricultural Herbicides


Roundup® brand agricultural herbicides need to get on the plant, in the plant, and throughout the plant for good weed control. In other words, they need good coverage, absorption, and translocation. The following are some reminders and considerations when using a Roundup® agricultural herbicide, such as Roundup PowerMAX® and Roundup WeatherMAX®.

Coverage, Absorption, and Translocation
Coverage is often compromised by the weed or crop canopy. Coverage can be improved by choosing the proper nozzles, adjusting the boom height, and spraying it an appropriate ground speed. Use of spray volumes that range from 10 to 20 gallons per acre generally provides good coverage on target weeds.

Weeds need to be actively growing for good absorption and translocation of the herbicide. Environmental conditions can affect absorption and translocation. Dry weather causes weeds to have thickened cuticles, which are harder for herbicides to penetrate. Dry weather can also increase dust that can bind with glyphosate, the active ingredient in Roundup® agricultural herbicides, making it less available for absorption into the plant. Adjusting the rate and using the proper additives can help under these conditions.

Translocation requires actively growing weeds with a good plumbing system, the xylem and phloem. Mechanical damage from tillage, planting or spray equipment can compromise the plumbing. Tillage that injures but does not kill the weeds can make them appear shorter because much of the plant is below the soil surface. Planters and drills can cause the same effect. Lack of weed control in sprayer tracks can be due to a restricted plumbing system of a plant and/or the presence of dust. Stem boring insects can also damage the plumbing, restricting translocation. When weeds injured by stem boring insects have been sprayed with a Roundup® agricultural herbicide, the portion of the plant above the insect damage should die. Below the insect damage, the weed often remains green and may regrow. Giant ragweed and marestail are two examples of weeds where this has been noticed.

Use the Right Rate
The rate for the field should be determined by the largest weed or the most difficult to control weed, not the most prevalent. If the field has predominantly 3 to 4 inch velvetleaf, but also contains a fair amount of 11 inch lambsquarters, the recommended rate would be 32 fl oz/acre due to the height of the lambsquarters (Table 1). 

General Recommended RatesAnnual weeds that are older and more mature or hardened-off may require 44 fl oz/acre even if they are less than 12 inches tall. Environmental stress, such as dry weather, can cause weeds to be short for their age, requiring a higher rate for good control. Tough to control annual weeds like common and giant ragweed and perennial weeds generally require the higher rates of 32 to 44 fl oz/acre. Check the herbicide label for application restrictions, and use full rates to help achieve complete control of existing weeds.

In-Crop Application RemindersAmmonium Sulfate (AMS)
AMS conditions hard water and can be added to the tank at 8.5 to 17 pounds (1 to 2% by weight) of spray grade AMS or equivalent rate of liquid AMS product per 100 gallons spray solution. Additional nonionic surfactant can also be added to Roundup PowerMAX® herbicide at 1 to 2 quarts per 100 gallons spray solution to improve control.

Making Re-Treatments
When re-treatment is necessary, allow time for weeds to recover and resume growth. Use the right rate of a Roundup® agricultural herbicide, considering weeds are older, taller, and will probably be even more difficult to control. If sprayer tracks were the problem, avoid the previous tracks. Weeds need to be actively growing for the best results.

Tank Mixtures
Labels for Roundup® agricultural herbicides include approved tank-mix partners. Tank mixtures that could cause antagonism and reduce the effectiveness of Roundup® agricultural herbicides should be avoided. Tank mixing with insecticides, fungicides, and nutrients or foliar fertilizers is generally not recommended.

Herbicide Mixing Order Application Timing

The timing of weed control can affect yield potential. Weeds should be controlled prior to 4 inches to help maximize yield potential. As the season progresses, it is also important to remember the label restrictions for maximum rates and growth stages for corn with Roundup Ready® 2 Technology, Roundup Ready® Corn 2, Roundup Ready® Soybeans, and Genuity® Roundup Ready 2 Yield® Soybeans (Figure 2).