PLOIODERMA NEEDLECAST ( Ploioderma lethale )
Ploioderma needlecast is a serious disease of Austrian Pine. This disease may cause severe stunting as well as needle discoloration and some premature defoliation where needles are heavily infected. Some trees may be killed by repeated severe infestations. Symptoms include yellow to brown spots which begin to show up in late winter or early spring on the previous year's needles. As the weather warms up in the spring, a portion of each infected needle quickly turns a straw brown color even though the base of the needle may remain green.
The most diagnostic feature is the appearance of tiny, elongate, black lines which are formed by fungal tissue and run lengthwise along the infected part of the needle. Beneath this fungal tissue lie the individual fruiting bodies, called apothecia. Several fruiting bodies may be found on a single infected needle. Once the apothecia are mature, and environmental conditions are sufficiently damp, they will shoot out spores to infect the new needles. Symptoms will not appear on the newly infected needles until late that winter.
Fig. 1. Apothecia of Ploioderma needlecast
To control Ploioderma, use a registered fungicide to protect new growth in the spring. Apply the first treatment when the new growth is about 2 inches long and the needles are just emerging from the fascicles. Once the fungus begins to produce spores, it may continue to do so for about 6 weeks, so two additional treatments, at about 14 day intervals, may be necessary to protect the new growth as it expands. Also, select nursery stock carefully, and inspect it for a few years after planting. Ploioderma may be missed on nursery stock, because symptoms may not have shown up before the stock was dug.
|Fig. 2. Tree infected with Ploioderma shown in early spring after elongation of new shoots has begun.||Fig 3. Closeup of branch with needles infected with Ploioderma|