Mixing Anti-Crusting Agents with Pre-emergence Herbicides: Effects on Stand Establishment and Weed Control

Kurt Hembree, Farm Advisor, Fresno County

Soils that tend to seal over or crust following planting by seed and sprinkler irrigation can lead to a significant decline in plant stand establishment and yield. While there has been research conducted looking at various "anti-crusting" agents, little information is known on the influence of mixing pre-emergence herbicides with these agents.

A study was conducted in 2001 to determine the impact of combining anti-crusting agents with Shadeout® on stand establishment and nightshade control in processing tomatoes. A grower's field was selected in western Fresno County that had a history of soil crusting and poor tomato stands. Plots were established in April and measured 3 beds-wide and 600' long. Five pre-emergence treatments were included in the study, replicated 4 times each. The treatments were applied in a 12" band over the seeded row. The treatments included Shadeout® alone at 2 oz/acre and Shadeout® tank-mixed with N-Cal Platinum® (20 gpa), phosphoric plus N-phuric acid (6 gpa each), and Thiocal (40 gpa). Untreated plots were also included in the study. All treatments were applied with a 3-row sprayer that delivered the spray in 50 gpa.

Processing tomatoes were planted on April 6 and the treatments were applied. Over-head sprinkler irrigation was used to incorporate the treatments within 3 days of treatment. No yields were determined in the study.

Tomato stand was significantly improved over all the other treatments when N-Cal Platinum® was added to the herbicide as a tank-mix partner (See table). There was an average of 1 tomato plant emerged every 2", compared to 1 plant every 4" in plots not receiving any anti crusting materials. The other anti-crusting agents did not fair much better than the untreated. The degree of soil crusting was evaluated visually to see how much effort was required to break through the soil surface. Soil in the N-Cal treatment appeared flocculated, with little to no evidence of sealing over. All other treatments varied in the degree of hardness of the soil surface and were fairly difficult to break through. Black nightshade control was best where Shadeout® was applied alone or with the N-Cal treatment. The use of acid and Thiocal treatments led to reduced nightshade control. It is known that Shadeout® activity is adversely affected by acidity, thus explaining the poor control.

While this work is preliminary, it appears that certain anti-crusting agents can be tank-mixed with Shadeout® following planting direct-seeded tomatoes to improve stand while maintaining weed control. It also appears that acid-based anti-crusting agents have an adverse effect on the activity of Shadeout®. Further studies need to be conducted to determine the influence of these and similar anti-crusting agents on stand establishment. Hopefully, this will lead to the reduction in the amount of seed needed to achieve a desired stand in soils that tend to crust.

*Based on a scale of 0 to 5; 0 = no observed crusting and 5 = severe crusting

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