Diagnosing And Treating Root Rot And Avocado Black Streak In Fruit-Producing Avocado Trees

The avocado is a delicate and sensitive tree. Even when growing in its natural environment--South Central Mexico and several other tropical locations in South America--an intense flood, cold snap, or drought can damage its delicate leaves, as can poor soil quality. This delicate nature causes many homeowners to shy away from growing them, even though they can be grown successfully in certain areas of the southern United States. If you've been struggling to grow your own avocado tree, help is on the way. Learn how to diagnose and treat common issues in fruit-producing avocado trees right here.

Root Rot

This is one of the most common problems with all avocado tree species. Whether potted or planted outdoors, the roots of an avocado tree are exceptionally sensitive to rot and mold, but the symptoms tend to manifest from the top rather than the base of the tree. To diagnose root rot, check each leaf on your tree, particularly across the top canopy. Are they small, deformed, stunted or otherwise lacking in color and texture? Young leaves have a tendency to drop off before they are even full-grown in this condition, so the first symptom you notice may be leaves on the ground. Also look for yellow, black or even brown edges on the leaves, especially shortly before they drop off.

If the symptoms match, first hold back water for at least a few days; overwatering is a significant contributor to root rot in avocado trees, and allowing the soil to dry out may help. Treat for parasites and mold immediately. If you can see spots of mold on the tree itself, spot-treat these with a moldicide or fungicide product for fruiting plants. Be sure to choose a product that's safe to use on food-based plants, not just decorative trees. If you can't see any outward signs of mold, your best bet is to either prune the tree back and have the soil professionally treated, or replant it in an area that isn't infested.

Unfortunately, avocado trees are extremely sensitive to repotting and replanting and many don't survive the move. If all else fails, start over in light, clay-mixed soil that's free of pests.

Avocado Black Streak

Also exceptionally common when growing avocados, both in South Central Mexico and beyond, avocado black streak can quickly take a tree from full of life to irreparable if not caught in time. Symptoms produced included yellowing leaves, sores on the tree's bark and trunk that produce a powdery, easily removed substance, early leaf drop, or even the eventual death of entire branches and sections of the tree. Lower leaves may drop off shortly after they begin growing in, never making it to their full size. In some cases, trees with ABS may have black mottling along the edges of leaves and leaf stems, too. Prevention is worth a pound of cure in this instance, as ABS is extremely difficult to treat once it takes hold. First, always maintain good irrigation strategies and a healthy soil PH. Most species of avocado do well in loose soil with a PH of between 6 and 6.5. Proper irrigation is also extremely important, but you must take care not to overwater as this can cause both root rot and ABS to flourish.

If ABS has already taken hold of your tree, start by treating the soil and testing its PH level. Irrigate the soil immediately with a 2-hour flush in spring, summer, and fall. Avoid heavy irrigation in winter and cold snaps, as you may end up correcting the ABS and creating root rot instead. The bad news is that ABS is caused by a currently unidentified organism; little is known about which treatment methods are more suitable than others. Reference to it goes back approximately 60 years, with most cases identified in the state of California. Treating the soil may help, but in most cases, starting over is the only way to recover. If you do choose to replant a new tree, start with fresh soil and avoid Guatemalan varieties, as they are thought to be more prone to the problem than others.

A Note on Irrigation

With the exception of overwatering and cold, moist soil, irrigation is an excellent way to aid your avocado tree in good health. As a general rule, hold back water during cooler winter months and deep water occasionally during hot summer months. To deep water, simply run a garden hose to the plant and turn it about 1/8th of the way on. Leave it to drip into the tree's roots for two to three hours. Alternatively, use a drip system with a gallons-per-hour rating of no more than 1/4-gallon. Irrigation is especially important if temperatures exceed 100F or if you experience a drought. Irrigation can also help to flush out excessive salt, a problem common in some mountainous regions and along both the Atlantic and Pacific coast.

Contact a tree maintenance company, such as Destiny's Tree Service LLC, if you need assistance.