By far, the most severe loss from scab occurred in the upper portion of the tree. In many orchards, this loss was mainly due to poor spray coverage in the upper portion of the tree, as scab control on the lower portion of the tree was often commercially acceptable or excellent. Lack of scab control in the upper canopy was not unique to the 1997 season. The same situation occurred in 1989, 1991, 1994, and 1995, all of which were years of moderate to high scab pressure. Thus, lack of coverage in the upper canopy is a major and frequently occurring problem. The problem is major because much of the fruit bearing surface is in the upper canopy. A high proportion of fruit being in the upper canopy is especially the case in cultivars with an upright growth pattern (for example, Stuart) and in overcrowded orchards.

On tall trees, poor coverage in the upper canopy occurs despite the type of sprayer used or sprayer speed. The tree is simply too tall for the sprayer. Because the tree continues to grow taller, the problem worsens each year. Improved sprayers will no doubt be developed but there is no assurance that they can be used to solve the tall tree problem.

Observations suggest that night spraying improves coverage in the tree tops. The best scab control that I observed in Albany, Georgia area during 1997 was in an orchard sprayed at night. Scab control in the upper canopy was much better than in similar orchards sprayed during the day. Scab control in this orchard was also good in 1995, again when spraying was done at night. An orchard in southeast Georgia historically has better scab control in the upper canopy than most orchards. This orchard is also sprayed at night. Night spraying, although more trouble, has two major advantages. One, wind speed is usually low which allows spray to travel to a greater height than with day spraying. Two, the cooler night time temperatures reduce the chance of the spray evaporating before it reaches the tree top. Although observations strongly suggest that night spraying results in better scab control than day time spraying, the observations have not been tested experimentally.

Even with night spraying, scab is not controlled in the top of very tall trees. Some growers are trying to solve this problem by aerial application of fungicides. Because ground application is also required, fungicide cost is substantially increased with aerial spraying. Experimental testing of aerial application of fungicides is needed. At least four questions need to be resolved. One, will aerial application improve scab control in the upper portion of the canopy? Two, what is the best fungicide (systemic or a combination of systemic and nonsystemic) to use? Three, what is the minimum fungicide concentration that will give control? Four, is aerial application cost effective?

Experimentally, the focus period for aerial application of fungicides should be the 6-week interval, June 1-July 15. Fruit scab that occurs within this interval will cause the most damage as showed by the classical work of T. R. Gottwald and P. F. Bertrand (Proc. Southeastern Pecan Growers Assn. 75:113-121). Fruit scab infection that occurs after July 15 is not very damaging and especially if fruit maturity is predicted to be early. Because aerial application is an additional and substantial cost, application should be based on a leaf wetness advisory. With a leaf wetness advisory, fungicides are applied only if needed. Thus, fungicide efficiency is maximized at minimum cost. Fungicide application based on leaf wetness requires strict timing and, for this reason, aerial application could be ideal.

Tall trees, as such, are not the only reason for poor fungicide coverage in the upper canopy. Overhanging limbs often block the spray and prevent it from reaching the upper canopy. This blocking effect is obvious in September following a season of high scab pressure. Scab control is decidedly better on the overhanging limb than on limbs directly above it. Furthermore, leaves of the over hanging limb are glossy compared with the dull sheen of leaves that were not sprayed or partially sprayed. The effects of blocking always show up during a moderate to high pressure scab year, for example, 1989, 1991, 1994, 1995, and 1997. Blocking is especially a problem with Schley. Characteristically, Schley has low hanging limbs with dense foliage. Some growers are removing low, blocking limbs on Schley. Initially, there was some concern that removing these limbs might substantially reduce marketable production. However, as indicated earlier, much of the production on a mature tree is in the upper portion of the tree and not on the over hanging limbs blocking the spray. Production on low, overhanging limbs becomes expensive during a heavy scab year.

Almost invariably, scab in the tree top is observed after it is too late to do anything about the problem. The late discovery occurs because of the difficulty of seeing the fruit in the tree top before late June or early July. Even then, scab cannot be readily observed from the ground. Scab control in the upper tree canopy can be evaluated by periodically cutting off a tall limb from a susceptible cultivar, such as Schley, and looking for scab. (If the limbs are removed from temporary trees, long-term rot and damage to tree structure is not a concern.) Limbs should be cut off in late April, late May, and in mid June. Cutting limbs off in April is especially important as this is an opportunity to evaluate spray coverage before fruit scab becomes a concern. If there is scab on the foliage at this time, steps to correct the problem need to be immediately taken. Even if there is only a trace of scab in April, efforts to improve fungicide coverage, timing, or both are urgent, as leaf scab is normally easier to control than fruit scab. Fruit scab is more difficult to control because of a subsequent increase in foliage density and rainfall. Because of the increased difficulty of control, reevaluating scab control in late May becomes very important. Evaluation in early June is important although scab may be devastating by this date. Cutting limbs off has an additional advantage in that preliminary assessment of fruit set can be made along with the scab evaluation.