Transpiration burn may sound like a used car deal gone bad, but it is a symptom of mite infestation that can significantly reduce your pear crop.
What is transpiration?
Transpiration refers to the way plants release water into the atmosphere through tiny openings, called stoma. Stoma are mostly found on the underside of leaves, but they also occur on stems and flowers. Stoma open and close to allow for the gas exchange necessary to photosynthesis [carbon dioxide in; oxygen out]. Transpiration also helps move plant nutrients, such as zinc, into and around within a plant.
The combined effects of plant transpiration and evaporation of water from the soil is called evapotranspiration. Maintaining the proper balance of water within a plant is critical to its health. When mites start feeding, that balance is threatened.
Types of mites
There are over 42,000 different types of mites in the world. They can be black, yellow, green, brown, or red. They are tiny. The most common mites in the San Francisco Bay Area include gall mites, spider mites, European red mites, and thread-footed mites. There are mites that prefer buds, mites that raise blisters (on plants), and mites that create a rust pattern. All mites have piercing mouthparts which are used to suck nutrient rich fluids from your plants. This can be a serious threat to plant health, especially in areas with scorching summers that are prone to drought.
Damage caused by mites
Mite feeding often causes stippling, tiny white or yellow spots, on leaves. Each of these spots represents a place where plant tissue has been pierced and the nearby fluids removed. Further feeding can lead to bronzing. As temperatures rise and mite feeding continues, transpiration burn can start killing leaves and reducing your crop.
Symptoms of transpiration burn
Transpiration burn occurs when mite feeding reaches critical levels. The accumulated water loss from mite feeding reaches a point where entire areas of the leaves die, leaving spots of dead brown or black tissue. This is referred top as transpiration burn and it is most commonly seen on pear leaves.
Transpiration burn halts photosynthesis and can lead to early leaf drop. Less leaf area means less photosynthesis, which results in smaller crops and unhealthy trees.
Preventing transpiration burn
A large, properly hydrated tree can lose up to 100 gallons of water a day during the peak of summer. Proper irrigation, using irrigation rings or soaker hoses, can prevent water stress to fruit and nut trees. This helps your trees counteract the damage caused by mites.
Mite control is tricky. These pests quickly develop resistance to chemicals, so pesticides don’t work. You can use a strong stream of water from a garden hose to displace mites. You can also buy predatory mites that hunt and feed on the mites feeding on your plants. Insecticidal soaps and oils can also be used, but care must be taken that these products don’s cause sunburn damage or other problems.
Keep your plants healthy and monitor them regularly for webbing and stippling, so you can deal with mite populations before they get out of hand.
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