University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Associate Professor Xavier Martini recently wrote an article In the Cold Hardy Citrus Connection about management of mites for fresh market citrus. Martini is an entomologist at the North Florida Research and Education Center. An edited version of his article follows.
Two types of mites mainly affect citrus production in North Florida: rust mites and spider mites.
RUST MITES
Rust mites are one of the biggest concerns for fresh market production because they directly damage fruits. Early damage consists of the destruction of epidermal tissues. As fruit enlarges, the destroyed epidermal cells fracture the skin, causing “sharkskin” damage. Damage to mature fruit creates a brown stain but does not destroy epidermal cells or the wax layer, leading to a polished look referred to as “bronzing.” Both types of damage considerably reduce the marketability of the fruits.
Photo by Betsy Martin
Rust mites are microscopic and not visible to the naked eye. They reproduce quickly, laying approximately 30 eggs in their lifetime and developing from egg to adult in just six days. Because of this fast reproduction and the damage occurring at the formation of the fruit, early detection is important.
A sampling plan should be established soon after the formation of the fruits. It is recommended to sample every two weeks in 10 locations per citrus block. In each location, sample four trees and two fruits per tree (80 samples total). Each sample should be taken directly from the fruit on all four quadrants (north, south, east and west) of mid-canopy fruits, by observing the presence of rust mites with a 14X zoom lens. For fresh fruit production, the recommended action threshold is an average of two mites per lens view.
SPIDER MITES
The red spider mite is the most common spider mite in North Florida and causes the most damage. Citrus red mites feed beneath the epidermal layer of cells, causing cell destruction and reducing photosynthesis.
Photo by Xavier Martini
Spider mites prefer dry weather and low relative humidity. They reach their peak during summer and are mostly found on the upper leaf surface of recently mature flush. All stages of the mites orient along the midvein.
Sampling for citrus red mites should occur with 25 trees selected randomly in each block. For each tree, sample one fully expanded leaf per quadrant, four leaves per tree. For fresh fruit, the recommended threshold is eight mites per leaf. Once the threshold is reached, chemical treatments are recommended.
Many insecticides have little to no efficacy on mites. It is beneficial to rotate modes of action to avoid the development of resistance.
The only pesticide that can be used repeatedly is petroleum oil, such as 435 oil. Petroleum oils can be combined with conventional miticides. However, they are slightly less efficient than conventional miticides. As citrus is attacked by a range of different pests, choosing a miticide that is also effective on other pests such as citrus leafminer or California red scale can be beneficial.
Source: UF/IFAS
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