Fall, Winter, and Spring Surveys

Fall Surveys

In the fall, when hardwood leaves change color, it is difficult to detect new SPB spots in mixed pine-hardwood forests. The yellow or red foliage of cypress trees in the fall also may be mistaken for beetle-infested pines. As a result, survey flights are usually discontinued until hardwoods have completely dropped their leaves.

Winter Surveys

Figure 14.-Winter spots in Virginia (Virginia Division of Forestry).

Figure 15.-Winter SPB spot in Texas.

The purpose of winter surveys is to locate overwintering SPB populations so that control can be applied before beetles disperse in the spring. Ground check priorities during winter surveys can be based on just two factors: number of affected trees and accessibility for control. Remember, SPB broods develop more slowly during the winter, often remaining within trees until after the foliage drops. Red crowns in a SPB spot during the winter, unlike those in summer, indicate that beetle broods are present.

The effectiveness of winter surveys for SPB varies among different geographic regions. Their activity restricted by cold temperatures, beetles in the Piedmont and Atlantic Coast States tend to remain throughout the winter in the same multiple-tree spots they occupied during the late fall. These spots become detectable when aerial surveys are resumed in December or January (fig. 14).

In the Gulf Coast, however, beetles in the fall often leave large spots to infest single trees scattered throughout the forest, and, in mild winters, may continue to infest new trees. Pines infested in winter maintain green crowns for 2-4 months, thus escaping observation during aerial surveys. In winter, even multiple- tree spots started in the fall . are easy to overlook on the Gulf Coast because the foliage color of infested trees does not change dramatically. Between December and April, infestations seldom show the yellow crowns

that clearly mark SPB spots in summer. At normal survey altitudes (1000-2000 ft), you may be able to see only the larger groups of bare and red-crowned trees (fig. 15). Most of the red-topped pines still contain SPB. But much of the beetle population in winter and early spring occurs in scattered single trees which elude detection. By flying slowly with a helicopter at low altitudes (100-500 ft), you have a better chance of seeing beetle-infested pines in winter along the Gulf Coast. At these low altitudes you may see off-color crowns of beetle-infested pines (fig. 16) that at higher altitudes would not be distinguishable from uninfested trees. Also, trees killed by SPB often have bark stripped by woodpeckers, which leaves them with highly visible white boles. Although effective, surveys by helicopter are costly and generally applicable only to high value stands.

Figure 16.-Helicopter view of scattered infested pines in winter.

Spring Surveys

Trees killed by beetles in late winter on the Gulf Coast can be seen during March and April. Even though early emerging beetles may kill large numbers of trees, new spots in spring seldom persist or expand. Temperatures in the spring are still too cool for continuous spot growth. This results in many scattered, short-lived spots in which groups of infested trees show the same foliage color.

Locating new SPB spots in early spring is difficult in mixed pine-hardwood stands: new foliage on hardwood trees makes them resemble SPB-killed pines with fading foliage. As conditions improve for long distance dispersal, however, beetles leave scattered brood trees to concentrate in expanding spots. These multiple-tree spots become easily seen by early summer in the Gulf Coast or by midsummer or later in the remainder of the South.

Because of these seasonal limitations, SPB observation surveys along the Gulf Coast are most effective from May to October. For States along the Atlantic Coast and in the Piedmont region, SPB surveys are practical during midwinter as well as throughout the summer.