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Phytophthora Foot Rot/Gummosis (fungus - Phytophthora spp.)

This is one of the more important pathogens of citrus in Texas. It primarily infects the roots and the trunk [Picture]. Infection of the trunk results in a dark, water-soaked areas, often with profuse exudation of a dark resin from the lesion [Picture]. The dead bark frequently sloughs off the wood in vertical strips. If the lesion encircles the trunk, girdling occurs, leading to the death of the tree. Trees killed by this fungus are defoliated and show an abundance of fruit [Picture].Trees with the bud union beneath or close to the soil and trees in poorly drained locations are especially susceptible to infection.

Phytophthora foot rot can be prevented through the use of resistant sour orange rootstock, budded 4 to 6 inches high, and planting at the proper depth in well-drained soil. Flood irrigation water must be kept below the scion and micro-irrigation emitters should be placed so that the trunk is not left wet for prolonged periods. Soil banks should be removed as soon as the danger of frost has passed. When tree wraps are used on young trees, trunks should be treated with a recommended fungicide and they should be inspected for bark damage or gumming if there has been fire ant activity.

Pruning and sprout removal are best done only in dry weather. Cultural activities that result in occasional trunk injury, such as disking or boom spray applications should be done at least 2 days in advance of irrigation.

Trunk lesions can be treated with fungicides. Severely damaged or unproductive trees should be removed from the orchard.

 

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