Nitrogen Fertilizer Solutions Providing Ancillary Weed Control in Cole Crops
AN-20 o Ammonium thiosulfate
AN-20, ammonium thiosulfate, and mixtures of these two materials can be used as N sources, while also providing ancillary weed control in broccoli, cabbage, and cauliflower. The amount of N per gallon of material, the rate at which it is applied, and the phytotoxicity of the material determines the crops on which these can be used.
All of these materials, when applied at the proper time and manner have the added benefit of ancillary control of many small (less than 3 inches) broadleaf weeds such as groundsel, pineapple weed, shepherdspurse, mallow, pigweed, hairy nightshade, chickweed, and many others. Poor or no control is obtained on lambsquarters, purslane, henbit, black nightshade, knotweed, sowthistle, malva goosefoot and grasses.
When using these N sources in foliar applications, follow cautions listed. Severe crop injury may occur if cautions are not observed.
General cautions for the use of nitrogen liquid fertilizer formulations are:
* Apply only after the crop has at least two true leaves. Application at between the 3rd and 4th true leaf stages is least likely to cause crop injury.
* Do not apply within 4 days of a period of cool, cloudy or rainy weather, or if free water is present on the leaves.
* Discontinue application if spray droplets do not roll off or "bead-up" on the leaves. This indicates a deficiency of adequate waxy cuticle, and may be a temporary condition due to rapid growth, cloudy or rainy weather, or more seriously, the lack of adaptability of the variety.
* Do not apply within 4 days after a foliar pesticide has been applied, or with any wetting agent.
* Use large nozzles to minimize misting and possible injury to the crop growing point.
* Direct the spray to the base of the crop with wide, low nozzles, or use crop shields whenever this can be done while still obtaining complete coverage of the weeds.
AN-20 fertilizer formulation:
This is a manufactured 20-0-0 formulation (containing 20% N) that may be applied at 50 to 70 gal product/acre as a foliar spray. This formulation weighs 10.55 lb/gal and contains 2.11 lb N/gal of product and would provide approximately 100 to 140 lb N/acre (but some N is lost through volatilization). Do not irrigate for 48 hours after application, but irrigate then to move the fertilizer into the root zone.
When this treatment is used as an N source and timed to provide ancillary weed control, subsequent N sidedressings should be reduced by a portion of the amount of N applied in the treatment.
To prevent crop injury, follow the cautions listed above.
Note: This formulation is different from a solution that could be prepared by dissolving ammonium nitrate in water. Such a solution would not have the same concentration or effect on weeds.
Note: Mixtures of AN-20 and ammonium thiosulfate (usually 1:1) can be made which will reduce the amount of N applied, provide some sulfur (compared to application of AN-20 only, and reducing the sulfur if only ammonium thiosulfate were to be used), and be as effective as either material alone. Application rates are still held at 50 to 70 gallons of the mixture per acre.
Ammonium thiosulfate:
This is a manufactured 12-0-0-26 formulation (containing 12% N and 26% sulfur) and weighs 9.33 lb/gal. It may be applied at 50 to 70 gal of product per acre as a foliar spray. This solution contains 1.12 lb N and 2.4 lb S/gal of product and would provide approximately 55 to 75 lb N/acre (some N may be lost through volatilization). At the application gallonage mentioned, about 150 to 168 lb S/acre are also applied. Do not irrigate for 48 hours after application, but irrigate then to move the fertilizer into the root zone.
When this treatment is used, subsequent N sidedressings should be reduced proportionately.
To prevent crop injury, follow the cautions listed above.