PEST CONTROL IN HIGH DENSITY APPLE ORCHARDS

Henry W. Hogmire
West Virginia University Experiment Farm
Kearneysville, WV

(Text of a presentation at the Annual Meeting of The Virginia/West Virginia State Horticultural Societies, Roanoke, Va., January 13, 1998.)

Tree row volume (TRV) spraying provides a means to match pesticide application to the target tree in terms of spray volume and pesticide rate. In the TRV concept, each tree row is treated as a rectangular box having a specific volume of foliage per acre. Foliage volume is determined from tree height, width, and row width (distance between rows). A standard size tree (19.5 ft high, 23.5 ft wide, 35 ft between rows) would have 570,521 cu ft of TRV per acre. A tree of this size was considered to require a spray volume of 400 gal per acre for a dilute application and 100 percent of the pesticide rate per acre. Spraying trees of smaller sizes in closer plantings should theoretically require a lower spray volume for a dilute application and lower rates of pesticides to achieve the same coverage and control. The following formula can be used to calculate the dilute spray volume needed for different tree sizes and row spacings: TRV Gallons/Acre = (Tree Height x Tree Width x 30.54)/Distance Between Rows. To determine the percent of the full pesticide rate per acre to apply, divide the TRV Gallons/Acre by 4.

An experiment was conducted in 1987, in cooperation with Dr. Ross Byers, to validate the TRV concept in terms of spray deposit on the following five Delicious planting systems (tree canopy height, tree width, distance between rows, % TRV): Lincoln canopy non-spur (2.5 ft, 7.5 ft, 12 ft, 12%), 3-wire trellis spur (8 ft, 5.5 ft, 12 ft, 28%), Dutch spindle spur (8 ft, 5.5 ft, 10 ft, 34%), 3-wire trellis non-spur (10 ft, 7 ft, 12 ft, 45%), and central leader semi-dwarf non-spur (11 ft, 12.5 ft, 20 ft, 52%). The Lincoln canopy represents a horizontal training system, whereas the other four plantings represent vertical training systems. All five planting systems were sprayed with a 0.01% liquid copper solution applied at 200 gal/acre with a Swanson 3-point hitch airblast sprayer. Leaves were sampled from each of five trees for each system and the deposit of copper was quantified by atomic absorption spectrophotometry. The copper deposit on the four vertically trained plantings decreased as % TRV increased (lower deposit on larger size trees). Even though the Lincoln canopy had the smallest canopy volume, it also had the lowest copper deposit, and therefore did not fit the TRV concept. The horizontal orientation of this canopy prevented good spray penetration with the airblast sprayer, resulting in very low copper deposit.

An experiment was conducted in 1989 and 1990 to validate the TRV concept in terms of pest control efficacy on ‘Delicious’ and ‘Golden Delicious’. Applications of fungicides (13 in 1989, 14 in 1990), insecticides (11), and miticides (3) were made at 44 percent of full rates in 1989 and 50 percent of full rates in 1990 to four of the five planting systems listed above (central leader semi-dwarf non-spur system was not included). Pesticides were applied with an FMC Economist airblast sprayer as complete sprays (both sides of the trees) at 100 gal/acre. The incidence of spirea aphids, European red mites and white apple leafhoppers were least abundant on the Dutch spindle system. The Lincoln canopy had the highest incidence of mites in 1989 and aphids in both years. Spray penetration with the airblast sprayer is inhibited by the horizontal orientation of the Lincoln canopy, and the excessive watersprout growth in this system is an ideal habitat that facilitates aphid increase. Aphid and leafhopper levels were similar on the two cultivars, however, mites were much higher on ‘Delicious’ than on ‘Golden Delicious’. Mites were also a little higher on the spur than the non-spur ‘Delicious’, even though the spur was a smaller tree. Insect damage to fruit, caused by tufted apple bud moth, plum curculio and tarnished plant bug, was the least on the 3-wire spur planting, with not much difference among the other systems. There were similar levels of damage on both cultivars. There were generally greater differences among systems for diseases than for insects. Disease damage from sooty blotch & fly speck, apple scab and rots was also the least on the 3-wire spur and highest on the Lincoln canopy. There was generally more disease damage on ‘Delicious’ than on ‘Golden Delicious’. A strong correlation was found between total fruit damage (insects and diseases combined) and TRV for the vertical systems. Percent fruit damage increased with increasing percent TRV in both years (more damage on larger size trees). Although the horizontal Lincoln canopy had the lowest TRV, fruit damage was comparable to the vertical system with an intermediate TRV. There was a change in the fruit damage ranking of 3-wire non-spur and Dutch spindle systems between 1989 and 1990. During 1989, the Dutch spindle system had a smaller TRV and lower level of fruit damage than the 3-wire non-spur system. Because of spring frosts in 1990, which reduced the Dutch spindle crop to a greater degree (lower location in intensive orchard planting), more growth occurred resulting in a larger TRV and more fruit damage than that on the 3-wire system.

In 1996 and 1997, a pest control experiment was conducted involving ‘Golden Delicious’, ‘York’ and spur and non-spur ‘Delicious’ on 3-wire trellis with TRV ranging from 28 to 51 percent of full size trees. Applications of fungicides (12), insecticides (11 in 1996, 10 in 1997) and miticides (1 in 1997) were made at 35 and 50 percent rates in 1996, and 50 and 100 percent rates in 1997. Applications were made as complete sprays (both sides of the trees) with an FMC Economist airblast sprayer at 75 gal/acre. Provado was applied for spirea aphid control, which was generally more effective at higher rates. In 1996, a 50 percent rate of this product provided better control than the 35 percent rate on ‘Delicious’ and ‘Golden Delicious’, but there was no difference on ‘York’ (Table 1). In 1997, the 100 percent rate (4 oz/acre) provided better control than the 50 percent rate on all cultivars. European red mites did not require control in 1996, but were controlled with Pyramite in 1997. There was no significant difference in control between a 50 and 100 percent rate (4.4 oz/acre) of this product on ‘Delicious’ or ‘York’ (Table 1). Provado was also applied for spotted tentiform leafminer control. In 1996, there was statistically no difference between a 35 and 50 percent rate of this product on all three cultivars, but there were slightly more mines with the higher rate (Table 2). It’s possible that the higher rates of other products in the spray program may have had a greater impact on parasites which attack leafminer. In fact, in 1997 there were more mines at the 100 than at the 50 percent rate on ‘Delicious’, whereas comparable control occurred with these two rates on ‘Golden Delicious’ and ‘York’ (Table 2). There was poor control of tufted apple bud moth with both a 35 and 50 percent rate of Confirm in 1996 (Table 3). Timing of the initial application for the second generation may have been a little too early, and the abundant rainfall may also have contributed to this lower level of control. Although there was less injury at the 50 percent rate, it was only significantly different from the 35 percent rate on ‘Golden Delicious’. There was much better control in 1997, with no difference between the 50 and 100 percent rate (18 oz/acre) on any cultivar (Table 3). Ziram and Topsin-M were applied for summer disease control, switching to Captan and Topsin-M for the last three applications. For rots (primarily bitter rot), there was no significant difference in control between 35 and 50 percent rates on ‘Delicious’ and ‘York’, but the 50 percent rate was better on ‘Golden Delicious’ in 1996 (Table 3). Rot incidence was especially high on both ‘Golden Delicious’ and ‘York’. There were much lower levels of rot in 1997, with no difference in control between 50 and 100 percent rates (Ziram - 3 lb/acre, Topsin-M - 8 oz/acre, Captan - 6 lb/acre) on any cultivar. There was also a high incidence of sooty blotch and fly speck in 1996, especially on ‘Delicious’ and ‘York’. There was no difference in control between 35 and 50 percent fungicide rates on these two cultivars, but the 50 percent rate was better on ‘Golden Delicious’ (Table 3). In 1997, there was virtually no incidence of these diseases with either rate. Certainly a big explanation for the lower disease incidence in 1997 was the dry season, as rainfall was only about 40 percent of what was received in 1996 (36.3 inches in 1996 and 15.1 inches in 1997 from April through September).

Research presented in this paper demonstrates that the TRV concept is valid based on spray deposit and pest control. Pest control on dwarf apples with 50 percent rates of pesticides was equal to that at 100 percent rates in 80 percent of the comparisons. Control with 35 percent rates was equal to 50 percent rates in 65 percent of comparisons. Weather and pest pressure are often more important variables in determining control success than the pesticide rate. The application of pesticides at 50 percent of recommended rates will provide a high level of insect and disease control on dwarf apple plantings in most situtations. Reducing rates below this level will require much greater attention to weather, pest pressure and application variables in order to be successful.

Means in a given column, for a given pest, followed by the same letter are not significantly different (Fisher’s protected LSD, P 0.05). 

Table 2. Spotted tentiform leafminer control (mines/5 minutes) with tree-row-volume pesticide rates on dwarf apple trees.

Means in a given column followed by the same letter are not significantly different (Fisher’s protected LSD, P 0.05).

Table 3. Insect and disease control on fruit (percent damage) with tree-row-volume pesticide rates on dwarf apple trees.

Means in a given column followed by the same letter are not significantly different (Fisher’s protected LSD, P 0.05).