Leaffooted Bug and Rust-Uncommon Problems in an Almond Orchard
UCCE Farm Advisor, Kern County
Deciduous Tree Fruits and Nuts
May 19, 2000
Leaffooted Bug and Rust - Uncommon Problems in an Almond Orchard
The first yield estimate for the 2000 Almond Crop is 670 million pounds which is a decrease of 160 million pounds from the 1999 crop year. There will be a second estimate in July for this year's crop. The first estimate is based on surveys sent to almond growers and handlers. However, the second estimate is more realistic as it is based on the number of nuts per tree from orchards in the main almond growing region of the state. The third estimate is the yield you will deliver to your handler. It is the yield that really counts.
There are many factors that can reduce the final yields. Insect damage during the growing season can be one of them. At the present time, the leaffooted bug, Leptoglossus clypealis, has infested orchards in Lamont, Shafter and McFarland. The varieties most affected by this insect are Sonora, Fritz, Padre and Mission. This insect feeds on young nuts early in the spring before shell hardening. The feeding is deep and can reach the embryo, and once the embryo is affected, will abort. The nut will then turn yellow and drop from the tree.
The feeding can also lead to internal and external gumming of the nuts. The leaffooted bug can continue feeding after shell hardening causing black spot, wrinkle and/or misshapen kernels.
The leaffooted bug can be recognized by the tiny leaflike enlargement on its hind legs. The narrow, brown body has a yellow zigzag line across its flattened back.
This insect is an infrequent pest and treatment thresholds for control haven't been developed, therefore, treatment should only be applied when high populations are present. The insecticide Sevin® can be used, however this pesticide can cause severe mite outbreaks.
Rust, Tranzschelia discolor, like the leaffooted bug is an infrequent problem in Kern County orchards. However, in some years it has severely defoliated some orchards in the Wasco-Shafter area. The most susceptible variety appears to be Carmel, but Merced, Sonora and Nonpareil are also susceptible.
April and May showers favor the spread and infection of rust in almond orchards. The most common symptoms are bright yellow spots on leaves, with red-brown spore-masses on the lower side of leaves. The first symptoms can appear in early June. If favorable conditions persist during June and July, new spores will infest new tissue. This will lead to premature defoliation in mid-summer.
Wettable sulfur at label rates has been effective in controlling this disease. However, to be effective, it should be applied before rust symptoms appear. Wettable sulfur should not be applied within three weeks of an oil spray.