Dothistroma Blight of Pines

Overview

Dothistroma blight is a foliar disease of a number of pine species throughout the Midwest. Austrian pine is the primary host plant in Missouri. This blight is caused by the fungus Dothistroma pini, which infects and kills needles. The disease makes pines in landscapes unsightly and successive years of infection can result in the decline and death of the tree.

Symptoms and Diagnosis

The earliest observable symptoms are dark-green bands and tan spots or bands on the mature needles. The spots and bands later turn reddish-brown. The needles will begin to die back from the tip, but needle bases usually remain green. From the time symptoms are first noticed to the time of needle browning may take 2–3 weeks. Infected needles will drop prematurely. Infection typically is most severe in the lower crown of the tree, closer to the inoculum that spreads from infected needles that have fallen from the tree.

Life Cycle

Dothistroma overwinters in infected needles. The infective spores are released during wet weather and dispersed by rain splash throughout the growing season. Because of the continual release of spores, infections can occur anytime from late April to late October. The fungus attacks the mature foliage; the current season's needles are resistant until they are fully mature. Symptoms on newly infected tissue are especially obvious in early fall.

Integrated Pest Management Strategies

1. Live with the disease but monitor yearly. This disease is slow to spread. Annual spraying is not necessary in residential plantings. Wait and see how serious the problem becomes in one season. Serious infections can be prevented in the next growing season with the use of fungicides.

2. Plant resistant pines. Research on Austrian pine has determined that some populations are highly resistant to Dothistroma. Ask for these at your local garden center or nursery. Choose other nonsusceptible evergreens.

3. Apply fungicides. Adequate control of Dothistroma blight can be achieved with one or two sprays in late spring using a copper-based fungicide such as Bordeaux mixture. The first spray in early to mid-May protects mature foliage. A second spray in mid-June will protect the current season's needles which are resistant until they are fully grown. Other protectant fungicides include chlorothalonil, Mancozeb, and pentachloronitrobenzene.

Organic Strategies

Strategies 1 and 2 are strictly organic approaches.

Pesticide Disclaimer: 

Always follow the product's label and ensure the product is effective against dothistroma. Not following the pesticide label before usage is a violation of federal law.