Managing Piedmont Forests To Reduce Losses From the Littleleaf Disease – Southern Pine Beetle Complex

R.P. Belanger – Principal Silviculturist, USDA Forest Service, Southeastern Forest Experiment Station, Athens, GA,
R.L. Hedden – Forest Entomologist, Clemson University, Clemson, SC, and
F.H. Tainter – Forest Pathologist, Clemson University, Clemson, SC.

Integrated Pest Management Handbook, USDA, Forest Service, Agriculture Handbook No. 649, March 1986.

In 1980, the Forest Service and the Cooperative State Research Service of the U.S. Department of Agriculture initiated the Integrated Pest Management Research, Development, and Applications Program for Bark Beetles of Southern Pines. This research/applications effort concentrates on pine bark beetles and associated tree diseases in the South. This is one in a series of Integrated Pest Management handbooks.

Evaluating Potential Problems

Rating the relative susceptibility of pine stands to littleleaf and SPB problems provides information that can be used to identify current or future hazard conditions, set priorities for management actions, and assess loss potential. The systems used to evaluate potential littleleaf and SPB problems in the Piedmont place heavy emphasis on site and soil conditions. These are important but neglected variables in assessing pest problems.

Littleleaf Disease
The most efficient way to evaluate a site for littleleaf hazard is to consider it's history. A site with no previous history of littleleaf is a low-hazard site. Sites with a history of littleleaf are high hazard (Anderson and Mistretta 1982). When mature and overmature shortleaf or loblolly pine are not present on the site, the rating system based on soil characteristics (Campbell and Copeland 1954) can be used (table 1). Soil characteristics are rated numerically and the scores totaled. Those sites totaling 75 or higher are expected to be free of littleleaf; scores of 51 to 74 indicate light to moderate hazard; a score of 50 or lower indicates high littleleaf hazard.

Table 1 – Numerical system for field-rating sites for littleleaf disease hazard based on soil characteristics (after Campbell and Copeland 1954)¹

¹High-hazard soils score 0 to 50 points; moderate-hazard soils score 51 to 74 points; and low-hazard soils score 75 to 100 points.

As a general rule, sites having severely eroded soil with a firm texture, a shallow permeable layer, or strong mottling of the subsoil are potentially high hazard for littleleaf and should be evaluated more critically.

Southern Pine Beetle The SPB risk-rating system described here has been developed specifically for Piedmont stand and site conditions (Karpinski and others 1984). It can be used in the office if suitable stand records exist or in the field by making a cruise. This system allows the user to rate a stand for the likelihood of an SPB attack, chance of spot growth, and potential for timber loss. Three variables are used to evaluate the risk of spot occurrence and the potential for loss (Fig. 8):

Figure 8 – Characteristics of high hazard little-leaf disease – southern pine beetle stands in the Piedmont (after Karpinski and others 1984).

• Pine component – Shortleaf pine is among the most susceptible species to SPB attack. Stands with 50 percent or more shortleaf pine have been shown to be very susceptible to SPB. The percentage of shortleaf pine in a stand can be determined by making visual estimates, conducting a cruise, or using appropriate stand records.
  
• Slope – In the Piedmont, more than 60 percent of all SPB infestations occur in areas where slopes exceed 10 percent. On such sites, erosion is a common cause of stress and may make trees more susceptible to SPB.
  
• Clay content – Clay soils are often associated with steep slopes or a history of sheet erosion. Littleleaf disease commonly occurs on these sites, stressing trees, and thus making them more susceptible to SPB attack. Any uncertainty about the identification of soil type or clay content in a stand can be resolved by a field visit. Pine stands growing on soils with at least 28 percent clay content are susceptible to SPB.

Determining spot occurrence (risk) – The following tabulation shows the procedure that can be used to determine the risk class for SPB spot occurrence in a stand:

Each risk class is assigned a numerical value (see the tabulation below). These values will be used in conjunction with others determined from "spot growth" on p.11 to estimate potential loss.

Stands with a low risk value (1) are the least susceptible to attack by SPB. Stands with a risk value of 3 are the most susceptible to attack, whereas those with moderate value (2) are intermediate in susceptibility.

Predicting spot growth (hazard) – The probability of an SPB spot increasing in size once it is established is directly related to stand density. Stands in which basal area is more than 120 square feet per acre are highly susceptible to spot growth. In dense stands, trees are close together, allowing dispersing beetles to find a new host easily. Pine basal area can be approximated using conventional approaches. The following tabulation shows how to determine the possibility of spot growth (hazard). Each hazard class is assigned a numerical value for purposes of estimating potential loss.

Estimating potential loss – Potential loss depends on the risk of an SPB spot becoming established in a stand plus the hazard of the spot growing once it is established. To determine potential loss, simply add risk value to hazard value:

Potential loss values can be used to determine the need for cultural treatments. Stands with loss values of 5 or 6 should be scheduled for silvicultural treatments first. Potential pest problems are greatly reduced in stands with loss values of 2 or 3.

When applying this rating system in the field, measurements should be made at several points. Then the risk, hazard, and potential loss calculated for each point should be averaged for the stand. When appropriate stand records exist, rating the stands in the office will yield a good estimate. If possible, ratings should be made when SPB populations are low, so that attention can be given to applying necessary cultural treatments to prevent losses rather than reacting to infestations when they may be too numerous to control or considerable loss has already occurred.

[  Contents  ]   [  Back  ]   [  Forward  ]   [  Home  ]