John R. Pyzner | 5/27/2005 2:15:16 AM
June Drop is a name that pecan growers have given to an event that occurs from mid June through early July. During this period, a large number of "nutlets" drop from pecan trees, explains LSU AgCenter horticulturist Dr. John Pyzner.
The drop occurs as the nutlets start to increase in size rapidly. Many pecan growers are nervous during the June drop, since the size of the drop varies in severity from year to year.
Pyzner says the three primary causes of the June drop are inadequate pollination, damage from the insect nut curculio and damage from the hickory shuckworm.
Inadequate pollination is often weather related. This type of drop is usually most severe following long rainy periods during late April and early May. Pecans are pollinated by wind-borne pollen. Rain removes much of the pollen from the air. Nutlets that drop from lack of pollination usually show no signs of injury.
"There was a very severe drop from lack of pollination in most areas of Louisiana last year because of prolonged spring rains," Pyzner says, but notes that the pollination drop is expected to be less severe this year, because the weather has been dry this spring.
A sign of nut curculio typically is a tobacco-looking stain near a small puncture injury on the nutlet. White legless worm larvae can sometimes be found by cutting into the nutlet. They can be so small it is difficult to spot them.
A sign of hickory shuckworm typically is a whitish blotch around a puncture on the nutlet. The blotch might be difficult to see, however, especially after a rain. The white shuckworms sometimes can be found by cutting into the nutlets. Shuckworm larvae differ from curculio larvae in that they have legs.
Shuckworm damage is often more severe in areas where the phylloxera insects have been a problem. Phylloxera form 1/4-inch to 1-inch diameter galls in which their eggs incubate. The first generation of shuckworm feeds inside phylloxera galls, and this helps build up the population for the second generation, which is a factor in the June drop.
Commercial pecan growers often spray insecticides the third week in June and the first week in July to control curculio and shuckworm. Growers may use only one spray or none if they have a heavy nut crop and have not had severe problems with curculio and shuckworms in recent years.
Control of nut curculio and hickory shuckworm is difficult for the home gardener since homeowners usually are unable to spray large pecan trees economically.
"A lot of pecans can be bought for the cost of spraying a yard tree," Pyzner remarks. For an alternative he suggests removing the fallen nuts soon after they drop to eliminate most of the curculio and shuckworm larvae. This can help control insect numbers in future years.
The LSU AgCenter horticulturist says June Drop sometimes can be a benefit. "It can be helpful in thinning nuts in years when pecan trees are overloaded," he says.
Thinning will improve nut quality during overloaded years and also can help reduce alternate bearing by evening out the high and low production years.
For related horticulture topics, look for lawn and gardening links at the LSU AgCenter Web site, www.lsuagcenter.com.