This article originally appeared in the May 2006 Ag News and Views newsletter.
It is hard to believe that summer is almost upon us. This has the potential to be a heavy pecan crop year, if the drought has not hurt things too badly. To ensure a good crop, many management decisions need to be considered over the next few months, including proper fertilization and insect and disease control.
Fertilizer should have been applied during late February and March, according to last year's leaf analysis. Leaf samples must be collected during July to determine the amount of fertilizer needed for the next year and to alert pecan producers to any nutrient deficiencies their trees may have. In the absence of a leaf analysis, a general rule is to fertilize with a complete fertilizer at a rate of 1 pound per inch in diameter, or 1 pound for each year of tree age. If fertilizer has not been applied and the trees have a good fruit set, you can go ahead and fertilize the trees. Just remember, if grass or weeds are growing around the trees, you will be fertilizing those as well. Also remember pecan trees have a higher requirement for zinc than other crops; therefore, a foliar application may be critical for maximum growth. Zinc should be applied beginning at bud break and repeated every 14 days through mid-June for a total of five applications. Insecticides and fungicides can sometimes be tank-mixed with these zinc sprays. Always follow the labels on the chemical to know if this is a safe practice.
This is an adult pecan weevil. Notice the long appendage that penetrates the shuck and shell of the pecan to lay eggs inside.
Insect and disease control are very important to maintain a good crop. Without them, flowers can abort and a large quantity of nuts can become damaged and be unmarketable. With extreme infestations, total crop loss can occur. The major insects and diseases to scout for are the pecan nut casebearer, weevil and pecan scab. Other insects and diseases can damage a crop, but these are the most detrimental.
When scouting for pecan nut casebearer during May, monitor nutlets for eggs and apply spray when most of the eggs are showing pink and beginning to hatch. Use traps to determine when to start monitoring nutlets or check the Oklahoma pecan casebearer model at agweather.mesonet.ou.edu/models/pecannut/.
Pecan weevil can be by far the most detrimental insect to a pecan crop. With heavy infestations, a large number of nuts can be damaged, resulting in an unmarketable crop. Weevils emerge from the soil starting in mid-July as the shells start to harden. Female weevils lay their eggs inside the kernel, and the larvae feed on the kernel. Trunk-mounted traps should be used to determine peak emergence, and insecticides should be applied to the trees before the weevils can lay their eggs.
Scab is the most serious disease in pecans and can infect both leaves and nuts. When infected, leaves drop off the tree, the size of nuts is reduced, quality is lost and proper shuck opening is prevented. Scab can be prevented with routine fungicide applications or by using the Oklahoma pecan scab advisor at mesonet.org/index.php/agriculture/category/horticulture/pecan/pecan_scab_advisor to determine when to spray.
If you have any questions about controlling these or other pests, call the Ag Helpline at 580-224-6500.