in this Issue
Wind Damage on Citrus
By Vincent Lazaneo
Citrus foliage twigs and shoots can be damaged by Santa Ana winds, like the blustery event earlier this month. The increased air flow combined with low humidity and low or high temperatures dramatically increases water loss from foliage which can damage tissue directly or indirectly by creating stress.
It’s best to wait a while after damage occurs to see if new growth develops. If twigs, shoots or branches are still bare after a few months, prune out the dead portions.
Drying winds can damage trees in three ways: through leaf fall, windburn, and scorch.
- Leaf fall - Leaves fall, separating where the blade is fastened to the petiole. The defoliated twigs usually survive and send out new leaves.
- Windburn - The affected leaves remain, roll, become brittle, and fall off in a few days. The twigs may send out new leaves.
- Scorch - Dry winds quickly kill and brown the leaves. The dead leaves remain attached to the twigs. Gum forms in the twigs and they soon die.
Injury from wind usually is on the exposed side of the tree only. Similar effects have been produced on the sides of trees exposed to hot sun or reflected heat during short warm periods in winter and early spring.
Water stress can also cause the soft interior tissue (mesophyll) of the leaf to collapse. The affected area first shows a slight change of color, then begins to lose chlorophyll and become dry. Some leaves turn light gray and then brown. If the area is invaded by certain fungi, it will turn dark brown to black.
Two types of twig dieback may result from water deficiency in plant tissue. In the first type, new growth during warm periods in the spring may come at a time when the soil is too cold to permit the roots to absorb enough water. This water stress causes gum to form in the water-conducting tissues. The flow of water is restricted, and the leaves on seemingly healthy twigs wilt, dry up, and remain hanging on the twigs.
In navel oranges, this type of dieback may occur after the crop is picked. While the fruit is on the tree, it acts as a reservoir, supplying water to leafy growth. Removal of the fruit (usually all picked at one time in commercial citrus) can result in stress which may lead to dieback.
In the second type of dieback, gum does not form in the stems. The leaves do not drop from the twigs until either the leaves or twigs are completely dry. This type of dieback affects larger limbs and branches than the first type. This severe form of dieback usually follows a period of excessive dryness during the preceding autumn.
There are several things you can do to protect citrus from wind damage. Check soil moisture when Santa Ana winds are predicted. If soil feels dry a few inches below the surface, water enough to wet the soil at least a foot deep.
Trees should not be treated with insecticide sprays when windy weather is expected or when trees need moisture. Soap and oil sprays remove some of the waxy covering from leaves and temporarily increase water loss.
Also, be careful not to apply excessive amounts of soluble fertilizer or manure which can increase soil salinity and make absorption of water by roots more difficult.
In some situations, it may be possible to construct a temporary windbreak with an old bed sheet or other material to protect the windward side of trees from severe desication.
Vincent Lazaneo Urban Horticulture Advisor for UC Cooperative Extension. He helped found the San Diego County Master Gardener Association more than two decades ago and serves as its advisor. He is the author of numerous articles on plants and pests that appeared in the San Diego Union-Tribune, California Garden and other publications