Early Blight Control in Organic “Valencia” Tomato with Copper Hydroxide
The majority of pest control in organic production systems relies greatly on management and cultural practices. The goal is to that minimize the opportunities for pest organisms to survive, reproduce, and increase to levels that can negatively impact crop production. However, some insects, weeds, and diseases are not easily stopped at the farm gate. They are migratory and are able to arrive from distant fields in spite of the best local practices. When environmental conditions that encourage an increase in a pest also hinder a producer’s ability to culturally control the problem, a crop failure can occur. Identifying and using organically certifiable crop protectants can provide some assistance in managing these pests. Copper containing products have been shown to provide moderate to good protection of non-infected foliage during an outbreak of disease caused by a range of bacteria and fungi. One of these products was tested here as a means of reducing incidence of early blight on an heirloom tomato.
To treat tomatoes planted in early June with copper hydroxide and measure the extent to which the product will control tomato early blight. Measurements taken include:
- Total number of mature, marketable tomatoes
- Total weight of mature, marketable tomatoes
- Number of premium and average quality (smaller sized or with a few cracks) fruit
- Amount of defoliation from foliar disease through the later part of the season
- Roy Brubaker (Village Acres Farm)
- Mifflintown, Juniata County, Pennsylvania
- Soil Type:
- Shaley clay loam
- Previous crop:
- cover crop of cereal rye/hairy vetch
- provided by cover crop
- Plot size:
- 6 plants in 1 row
- June 5, 2003
- Plant density:
- 4840 plants/acre
- Cover crop rolled with cultipacker, transplants set into slits
- Harvest date:
- August 23 – October 8, 2003
A field that was planted during the previous fall to a mixture of cereal rye and hairy vetch was rolled at maturity with a cultipacker during early June. Slits were cut into the rolled vegetation and tomato transplants were set several days later. Tomatoes were trained on a stake and twine trellis system. Plots consisting of 6 adjacent plants in one row were identified and treatments were assigned using a randomized complete block design with four replications. The four treatments consisted of: 1) control, 2) copper hydroxide (4 lbs/ac per sprayed application), 3) nitrogen (40 lbs/ac, once), and 4) a combination of copper hydroxide and nitrogen as defined in treatments 2 and 3. Nitrogen in the form of blood meal was applied to treatments 3 and 4 on August 8. Copper hydroxide (Champion® WP, NuFarm Agricultural Division) was applied at 4 pounds per acre formulated product (product contained 77 % CuOH) in 90 gallons water per acre via backpack sprayer weekly beginning on August 1. Mature red tomatoes were harvested twice weekly beginning on August 25. The last sampling occurred on October 8. Fruit were graded into average and premium quality classes, counted and weighed. Weeds were controlled by hand weeding or hoeing. A visual estimation of plant canopy was measured on September 18.
The rainfall was above average during the duration of the growing season. Frequent rains and extended hours of high humidity were favorable for disease development and warranted weekly applications of the copper hydroxide. Foliar symptoms of early blight were present prior to when harvesting began. Overall, tomato yields were good; ten harvests of fruit were taken prior to October 8 when the trial was concluded. Adding nitrogen did not influence the overall fruit yield or count, or the percent premium tomatoes that were harvested. For subsequent analyses, nitrogen only (treatment 3) results were combined with control results and nitrogen plus CuOH (treatment 4) data were combined with the CuOH alone treatment.
The use of CuOH increased the quality and quantity of leaf area. The differences were easy to see from the time fruit harvest began in late August. The loss of leaves to disease steadily took its toll on unprotected plants. Visual estimates of productive leaf area during mid September revealed that the remaining leaf area expressed as an estimated percentage of a full, non-diseased canopy was approximately 70 percent where copper was used and 11 percent in the untreated plots.
Total and premium fruit counts for the control and CuOH treated are presented in figure 1. The stress from the disease caused some premature ripening of fruit during the early third of the harvest season. However, the early production deficit was more than offset with increased production of total, and especially premium quality fruit, during the later two-thirds of the harvest season.
Copper hydroxide is not recognized by conventional tomato growers as being especially effective in controlling early or late blight on this crop. Numerous other synthetic products are better protectants against this disease. Organic growers are limited in their choices for a means to manage this air-borne disease that does not respect farm boundaries. While the level of control observed here would be considered by many conventional growers as being unsatisfactory, compared with the alternative of doing nothing, use of this type of product was shown to be a very cost-effective means to reduce the severity of early blight. Regular use of copper hydroxide in this trial resulted in extended canopy life, more total fruit, and more premium fruit being harvested and marketed. A response of this magnitude would be unlikely during drier seasons where conditions would be less conducive for the regional and local spread of the fungus.