Fusiform Rust: What's that orange stuff on my pine tree?

Just last week, I noticed the galls on the pine trees in my back yard started bursting open with the bright orange spores of fusiform rust. Fusiform rust is a damaging disease in landscapes and forests of the South. The most obvious symptom is spindle-shaped swellings or galls on the branches or trunks of pine trees.

Fusiform rust is caused by the fungus Cronartium quorum f. sp. fusiforme. Like many rust species, this fungus produces five different spore types and completes its life cycle on two different hosts: pine and oak.

During the spring, the fungus produces bright orange spores like the ones I observed on the galls. Typically, these spores are produced from late March to mid-April. Wind-blown spores infect newly formed leaves of several oak species, especially water, willow, and laurel oaks. Symptoms on oak are not conspicuous and usually the tree is not harmed. The fungus produces a different type of orange spore on the under-surface of oak leaves from late April through the middle of June. These spores are then wind-blown to nearby pines where they create new infections, causing new galls and continuing the cycle.

Pine trees are highly susceptible to Fusiform rust when young and infections that occur within the first 5 years of growth usually result in death. Later, main stem cankers can girdle and kill the tree or reduce its value. Stems with cankers are weak and susceptible to wind and ice breakage, and galls easily catch fire and stay afire. Secondary infections by the pitch canker fungus (Fusarium moniliforme var. subglutinans), black turpentine beetles (Dendrodoconus frontalis) and coneworms (Dioryctria spp.) aggravate the tree’s weakened condition, causing further damage.

Over the years, fusiform rust has become an increasing problem, particularly in pine plantations. Loblolly and slash pines are the most susceptible tree species. Longleaf is fairly resistant and shortleaf is highly resistant.

Management options include spraying fungicides, planting longleaf or shortleaf pines in areas with histories of severe rust infections, pruning branches with rust galls less than 15 inches from the stem, eliminating nearby oak hosts, and using rust-resistant clones.

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Red Bay Ambrosia Beetle Found in North Carolina!

The North Carolina State University Plant Disease and Insect Clinic, in communication with U.S. Department of Agriculture and North Carolina Department of Agriculture & Consumer Services, has corroborated the presence of red bay ambrosia beetle in North Carolina. This tiny exotic beetle was first detected in North Carolina this March, in Bladen County, by the North Carolina Forest Service.

Red bay ambrosia beetle transmits laurel wilt pathogen.
(Image Michael C. Thomas, Bugwood)

The red bay ambrosia beetle, Xyleborus glabratus, and the fungus Raffaelea lauricola, together constitute an insect/disease threat.

The beetle transmits the fungus which causes the disease known as laurel wilt. The combination is generally fatal to red bay, which is an important maritime forest species and is also sometimes found in the landscape. The decline of red bay may have secondary implications for some animals and other plant species.

Other plants in the laurel family, including sassafras, are also susceptible to the fungus. This disease complex a serious threat to the avocado industry in Florida.

Symptoms of laurel wilt.
(Images James Johnson, Bugwood)

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More information on Laurel Wilt will be presented in tomorrow's Plants, Pests, and Pathogens elluminate session.

Herbicide Injury to Tomatoes

"Classic" Glyphosate Symptom

Recently, the clinic has received several tomato plants with symptoms of herbicide damage. Glyphosate (found in products like Roundup) causes very distinctive yellowing symptoms at the base of tomato leaflets.  Broad-leaf weed killers (2,4-D type herbicides) cause stunted and deformed new growth, and whipping and curling of the leaves.  

2-4 D Type Injury 

Tomatoes are very sensitive to herbicide injury and damage can be severe.  In extreme cases, simply touching tomato plants with herbicide-contaminated hands or clothing can cause injury. 

Spray drift is an important source of herbicide damage. Sometimes symptoms appear in a gradient pattern, with plants closest to source being more affected than those further away. 

Be careful to prevent herbicide drift into home gardens, farms, or greenhouses where tomatoes are growing. To reduce the chances of spray drift, do not apply herbicides near these areas on windy days.  

Glyphosate Drift in Greenhouse

Some herbicides are formulated to provide season-long protection against weeds. Planting sensitive crops too soon after using one of these herbicides can cause injury. Check the product label to see when it is safe to replant following herbicide application.

Glyphosate Injury

Sometimes farmers and home gardeners report problems in vegetables and flowers after applying hay, manure, grass clippings, compost, or other amendments to soil.   Symptoms include poor seed germination, twisted, cupped, and elongated leaves, and misshapen fruit. Young plants may die and yields may be reduced in mature plants.  This damage can be traced to herbicide carryover in the soil amendment.  For more information on herbicide carryover in soil amendments, click here.