Sapstreak Disease (Ceratocystis coerulescens (C. virescens))
Sapstreak disease can be a serious problem in the sugarbush. The causal organism is one of the most common stain fungi of northern hardwood logs and bolts. It can enter and kill wounded trees. The primary avenues of infection are root and buttress injuries made by skidding or sap hauling (Fig. 103). Recent observations also suggest that trees can become infected through stumps created when sprout clumps are thinned (Fig. 104). Outbreaks of sapstreak always have been associated with logging or with sugaring. There is no evidence that broken branches, insect injuries, or even tapholes are suitable sites for infection to being.
A sparse crown usually is the first sign that a sugar maple tree has sapstreak. Leaves often are one-half or less than normal in size (Fig. 105). Sometimes, trees die suddenly. In fact, trees without symptoms during one year may fail to leaf out the next; others may succumb within a year or so. By contrast, some trees may linger for many years, showing progressive dieback before they die. Some may even recover.
Wood of buttress roots and lower stems has a stain with a unique color and pattern. Freshly exposed stain is moist, and drill shavings from such wood will be "mealy" in consistency and discolored compared to clean, white shavings from healthy wood. The stain is yellowish-green, bordered by a thin dark green margin (Fig. 106) It contains flecks or streaks that are reddish when fresh. Soon after exposure to air, the stain darkens and the red flecks become less distinct. The dark stain then fades to a light brown. In cross sections, the stain appears to radiate outward toward the bark (Fig. 106). Cankers develop where the cambium comes in contact with the spreading stain column.
Most trees affected by sapstreak are located along trails where logs have been skidded or sap has been hauled. The more heavily used the roadway, the more likely it is that adjacent trees will be wounded. More diseased trees have been observed in sugarbushes where buckets are used than where tubing is used. This reflects the greater number of wounds inflicted during the many trips to gather sap.
Sapstreak trees often occur in groups, sometimes close to the sugarhouse (Fig. 107). Such localization could result from the pathogen being carried from diseased to healthy trees by ground-inhabitating organisms (insects, millipedes, etc.), from wounding of groups of trees at specific times, or from interaction with other root pathogens known to attack and kill trees in groups. Nearly all trees killed by sapstreak also are severely attacked by one or more root fungi (Armillaria and/or Xylaria) (Figs. 108, 100)
Because the sapstreak fungus often grows and produces spores on the ends of bolts cut from diseased trees, piling wood from diseased trees near the sugarhouse may serve to build high concentrations of inoculum (spores and other fungus materials that can spread disease). Since such buildups cold increase the chances of infection in nearby trees, fuel wood from trees killed by sapstreak should be removed from the sugarbush promptly and used elsewhere.
Management of these vascular diseases should focus on reducing injuries to roots, buttress roots, and lower stems, and preventing an increase of the vascular pathogens and the commonly associated root pathogens.
For both sapstreak and Verticillum wilt it is of paramount importance to avoid injuring roots and lower stems when gathering sap, hauling wood, or skidding logs. Injuries can be reduced by using the same well-placed trails each year, the smallest machinery possible, and tubing systems rather than buckets. These measures are particularly important on steep, slippery slopes. Because trampling injuries by cows or horses also have been associated with incidents of sapstreak, these animals should not be allowed to graze the sugarbush. And, as mentioned earlier, prompt removal from the sugarbush of wood from sapstreak-infected trees will help reduce the buildup of infectious inoculum.