PR-410: 1998 Fruit and Vegetable Crops Research Report
Introduction • Tree Fruits • Small Fruits • Vegetables • Diagnostic Laboratory • Appendix A
Although apples are the principal tree fruit grown in Kentucky, the hot, humid summers and heavy clay soils make apple production a more difficult task for growers in this state than in many major apple-producing regions where soil and climate are more favorable. Poor tree survival, due to Kentucky’s heavy clay soils, has also limited plum production. Peach production is also erratic as a consequence of the extreme temperature fluctuations that occur in the winter and spring. In spite of these challenges, productive orchards are one of the highest income-per-acre enterprises suitable for Kentucky’s upland rolling soil, and they also have a low potential for soil erosion. Kentucky still imports more apples than it produces; however, the strong market for peaches continues to encourage peach production. Continued identification of improved rootstocks and cultivars is required for growth of the Kentucky fruit industry. For these reasons, Kentucky continues to be a cooperator along with 39 other states and 3 provinces of Canada in the Cooperative Regional NC-140 Project: Rootstocks and Interstem Effects on Pome and Stone Fruit.
Scions of known cultivars on various rootstocks were produced by commercial nurseries and distributed to cooperators for each planting. The University of Kentucky Research and Education Center at Princeton (REC) has five NC-140 rootstock plantings:
Except for the 1990 apple cultivar/rootstock planting, trees of each rootstock were randomly allocated to blocks (rows) in a randomized block design (i.e., each rootstock appears once and at random within each block). In the 1990 apple cultivar/rootstock planting, trees of each cultivar/rootstock combination were allocated to the blocks in a split-plot design (i.e, groups of 6 trees [each on a different rootstock] of each cultivar were randomly allocated to each block). Soil management is a 6.5 ft herbicide strip with mowed sod alleyways. Trees are fertilized and sprayed according to local recommendations (1,2). Yield, trunk circumference, and maturity indices such as soluble solids are measured annually for each planting.
The winter of 1998 in Kentucky was mild, but late spring frosts reduced some of our apple and plum crop. This was followed by an extremely wet spring and a very dry late summer and fall. Fruit generally had excellent quality, as there was no extreme pest pressure.
The 1990 Apple Cultivar/Rootstock Planting continues the evaluation of some of the promising rootstocks identified from previous trials at UK, REC, while also evaluating cultivars/rootstock interactions. This planting is also our first trial to be trained to the Dutch slender spindle system and supported by electrical conduit fastened to a wire trellis. This is one of a number of orchard systems that have been developed in Europe in order to reduce labor requirements and to enhance early production. Eastern and midwestern growers are rapidly adopting this production technique, and it is appropriate that UK should provide our growers with information on this system’s performance. The chief advantage of this system is early production with reduced labor inputs. Early production allows growers to quickly establish orchards with newer, more profitable cultivars.
One hundred sixty-one trees of a possible 180 are in our test because three cultivar-rootstock combinations (Golden Delicious/EMLA M.9, Jonagold/Bud.9, and Liberty/Ott.3) and one tree of Liberty/Bud.9 were not available for this planting. A trellis system was constructed in 1992. Based on foliar analysis and visual observation of vegetative growth, no nitrogen was applied in 1993-98. Vegetative growth is now in the high normal range. With this controlled vigor, the surviving trees are developing nicely. All pest-control decisions are based on IPM procedures, the same as used by our more progressive growers. Fire blight was very light in 1998. Nevertheless, 79 of the 161 planted trees (49.1%) have not survived, and significant differences in mortality by rootstock and cultivar were observed (Tables 1 and 2).
Both rootstock and cultivar significantly influenced dropped fruit, average fruit weight, cumulative yield and one of the fruit maturity indices, fruit pressure, (Tables 1 & 2). Percent soluble solids, the other maturity indicator that was measured, was significantly affected by cultivar (Table 1), but not by rootstock. 1998 yield, picked fruit, and trunk circumference varied significantly by rootstock, but not by cultivar (Table 2). Significant cultivar-by-rootstock interactions were only observed for dropped fruit and average fruit weight (Table 3).
This planting is located on a farm of a commercial apple producer in Somerset, which is about 200 miles east of the REC at Princeton. The planting provides us with a comparison of rootstock performance between western and south central Kentucky. To date, differences in mortality have not been statistically significant. Three out of eight trees on CG.202 and CG.210 have died. Four trees on CG.30, CG.222, and CG.13 and 2 on M.7 have also died. Statistical differences in the analysis of variance were not observed for trunk circumference, theoretical cumulative and 1998 yield, or number of rootsuckers (Table 4). The deer pressure contributes to the poor survival rate.
The 1994 semi-dwarf apple rootstock planting is the first trial at this station to be trained to the French vertical axe system. It also includes a number of new stocks, along with some that have performed well in previous plantings at UK, REC. This planting was established as planned, except for the substitution of B.9 for P.1. Trickle irrigation and a trellis system similar to the one in the 1990 apple planting were constructed in 1995. The mortality of trees on M.26 (10% survival) differed significantly from trees on the other 5 rootstocks (100% survival for trees on CG.11 and 90% for the others). There were no differences in the maturity indices (% soluble solids or pressures) or in the weight of dropped fruit, but trunk circumference, the number of rootsuckers, cumulative yield, 1998 yield, and picked fruit varied significantly by rootstock (Table 5). Trees on CG.13 have made the most growth. Crop load was adjusted so as to not exceed 10 fruits per cm2 of trunk cross-sectional area as per NC-140 protocol.
Poorly drained clay soils typically found in Kentucky have limited plum production. Rootstocks recently developed in France on soils similar to ours offer the potential for expanding the fruit industry in Kentucky to include this crop. To date, three trees on Julian A, five on Citation rootstock, and two on Myrobolan seedling have died, probably as a result of winter injury. All others (86%) are alive. Statistical differences in the analysis of variance were observed for cumulative yield, 1998 yield, number of root suckers, and trunk circumference, but not for fruit size (Table 6).
Peaches are one of the most popular fruits in Kentucky. The strong market for this crop continues to entice growers to plant trees in spite of the fact that one can expect erratic production due to the extreme temperature fluctuations that occur in the winter and spring in this state. A rootstock that is more suitable to Kentucky’s climate than ones traditionally used would be of great value to the fruit industry in the state. A rootstock that could significantly delay bloom would change the future of the Kentucky peach industry. To date, 75 of the 94 trees planted are alive (80% survival). Statistical differences in the analysis of variance were observed for bloom date, cumulative yield, 1998 yield, and average fruit weight (Table 7), but not for the number of rootsuckers, trunk circumference, or fruit pressure and soluble solids.
The NC-140 plantings are of utmost importance to Kentucky for gaining access to and testing new rootstocks from around the world. The detailed and objective evaluation of these rootstocks will provide growers with the information needed to select the most appropriate rootstocks for their needs when they become commercially available in the future. The 1990 Apple Cultivar/Rootstock Planting and the 1994 Apple Rootstock Planting will provide us with needed information on the adaptability of the slender spindle and vertical axe systems to trees grown on our fertile soils. The 1993 CG-Liberty Apple Planting is an off-station cooperative effort between the University of Kentucky and a commercial grower and provides us with a way to compare rootstock performance between western and south-central Kentucky. The 1990 Plum Planting should provide us with needed information to determine if there are suitable rootstocks for growing plums in western Kentucky’s wet clay soils. The 1994 Peach Planting should provide us with needed information to determine if tree survival, winter hardiness, and cropping frequency can be improved by using any of the recently developed rootstocks.
The NC-140 rootstock plantings are regularly used as demonstration plots for visiting fruit growers, extension personnel, and research scientists. The research data collected in these trials will help to establish base-line production and economic records for the various rootstock combinations which can be later utilized by orchardists in Kentucky.
| Table 1. 1998 Cultivar Results -- NC-140 1990 Apple Cultivar/rootstock Planting1 | ||||||||||
| Cultivar2 | Cumulative Yield per Live Tree (lb) | Picks (lb/tree) | Drops (lb/tree) | 1998 Yield (lb/tree) | Average Fruit Wt (oz) | Mean Pressure of Blush & Offsides (lbs) | Percent Soluble Solids | Number of Suckers | Trunk Circum. (in) | Percent of Trees Alive |
| Liberty | 326.3 | 35.3 | 4.4 | 37.5 | 4.2 | 23.3 | 12.9 | 0.7 | 10.2 | 69.0 |
| Golden Delicious | 321.9 | 30.9 | 19.8 | 50.7 | 5.6 | 17.0 | 14.8 | 0.5 | 11.3 | 40.0 |
| Jonagold | 257.9 | 19.8 | 15.4 | 37.5 | 7.1 | 17.6 | 14.6 | 0.4 | 12.0 | 30.0 |
| Rome | 251.3 | 17.6 | 11.0 | 26.5 | 8.7 | 21.4 | 13.5 | 0.0 | 11.1 | 41.7 |
| Empire | 194.0 | 17.6 | 4.4 | 22.0 | 5.0 | 21.0 | 12.1 | 1.8 | 8.9 | 72.2 |
| Mean | 262.4 | 24.3 | 8.8 | 33.1 | 5.7 | 20.7 | 13.2 | 0.9 | 10.3 | 50.9 |
| LSD (.05) | 79.4 | 15.4 | 6.6 | 19.8 | 0.7 | 1.4 | 1.3 | 0.7 | 1.3 | NA |
| 1University of Kentucky, Research and Education Center, Princeton, KY. 2Arranged by cumulative yield in descending order. | ||||||||||
| Table 2. 1998 Rootstock Results -- NC-140 1990 Apple Cultivar/Rootstock Planting.1 | |||||||||
| Rootstocks2 | Cumulative Yield per Live Tree (lb) | Drops (lb/tree) | Picks (lb/tree) | 1998 Yield (lb/tree) | Average Fruit Wt. (oz) | Mean Pressure of Blush & Offsides (lbs) | Percent Soluble Solids | Trunk Circumference (inches) | Percent of Trees alive |
| M.26 EMLA | 390.2 | 13.2 | 28.7 | 41.9 | 6.8 | 19.7 | 12.6 | 14.8 | 56.7 |
| M.9 EMLA | 352.7 | 4.4 | 30.9 | 35.3 | 5.3 | 22.4 | 12.4 | 13.0 | 41.7 |
| Ottawa 3 | 330.7 | 15.4 | 22.0 | 37.5 | 5.4 | 19.6 | 14.5 | 12.8 | 25.0 |
| Bud.9 | 260.1 | 11.0 | 26.5 | 37.5 | 5.9 | 20.8 | 13.7 | 9.4 | 87.0 |
| MARK | 152.1 | 6.6 | 13.2 | 19.8 | 4.8 | 20.9 | 13.6 | 7.1 | 50.0 |
| P.22 | 138.9 | 6.6 | 17.6 | 24.3 | 5.3 | 21.1 | 12.9 | 6.5 | 46.7 |
| Mean | 262.4 | 8.8 | 24.3 | 33.1 | 5.7 | 20.7 | 13.2 | 10.3 | 50.9 |
| LSD (.05) | 79.4 | 4.4 | 11.0 | 13.2 | 0.5 | 0.9 | 1.0 | 1.78 | NA |
| 1University of Kentucky, Research and Education Center, Princeton, KY. 2Arranged by cumulative yield in descending order. | |||||||||
| Table 3. 1998 Results -- NC-140 1990 Apple Cultivar/Rootstock Planting.1 | ||
| Cultivar/Rootstock Combination2 | Dropped Fruit per Live Tree (lb) | Average Fruit Wt. (oz) |
| Liberty/M.26 | 2.2 | 4.0 |
| Liberty/M.9 | 4.4 | 4.7 |
| Golden Delicious/Ottawa 3 | 35.3 | 5.4 |
| Golden Delicious/M.26 | 22.0 | 7.2 |
| Rome/M.26 | 11.0 | 9.0 |
| Jonagold/M.26 | 28.7 | 8.1 |
| Empire/M.26 | 6.6 | 5.6 |
| Liberty/Bud.9 | 2.2 | 4.3 |
| Golden Delicious/Bud.9 | 22.0 | 5.1 |
| Jonagold/Ottawa 3 | 13.2 | 5.8 |
| Rome/M.9 | 2.2 | 8.7 |
| Rome/Bud.9 | 13.2 | 9.1 |
| Empire/Ottawa 3 | 2.2 | 4.2 |
| Empire/M.9 | 6.6 | 5.0 |
| Empire/Bud.9 | 4.4 | 5.1 |
| Jonagold/P.22 | 13.2 | 8.5 |
| Golden Delicious/MARK | 8.8 | 5.1 |
| Liberty/MARK | 6.6 | 3.9 |
| Liberty/P.22 | 4.4 | 4.2 |
| Empire/MARK | 4.4 | 4.7 |
| Rome/MARK | 6.6 | • |
| Rome/P.22 | 15.4 | 7.1 |
| Jonagold/MARK | 6.6 | 6.7 |
| Empire/P.22 | 4.4 | 4.7 |
| LSD (0.5) | 11.0 | 1.3 |
| 1University of Kentucky, Research & Education Center, Princeton, KY. 2Arranged by cumulative yield in descending order. | ||
| Table 4. 1998 Results 1993 -- NC-140 CG-Liberty Apple Rootstock Planting.1 | ||||
| Rootstock2 | Theoretical Cumulative Yields3 (lb/tree) | 1998 Yield (lb/tree) | 1998 Trunk Circumference (inches) | Number of root suckers4 |
| CG.030 | 127.9 | 79.4 | 11.2 | 1 |
| CG.202 | 101.4 | 55.1 | 8.4 | 1 |
| CG.222 | 101.4 | 59.5 | 10.9 | 0 |
| CG.210 | 94.8 | 63.9 | 12.7 | 2 |
| M.7 | 77.2 | 46.3 | 10.4 | 4 |
| CG.013 | 70.5 | 66.1 | 10.7 | 9 |
| Mean | 97.0 | 59.5 | 10.6 | 2 |
| LSD (.05) | 75.0 | 46.3 | 3.5 | 8 |
| 1University of Kentucky, Research & Education Center, Princeton, KY. 2Arranged by theoretical cumulative yield in descending order. 3Theoretical cumulative yield was calculated by summing the theoretical yield for 1996 and 1997, and the 1998 yield. Theoretical yield for 1996 and 1997 was calculated by multiplying the number of fruit on each live tree in this planting by the average weight per fruit from `Liberty' trees in the 1990 apple planting (125 grams and 121 grams for 1996 and 1997, respectively). For 1997, yield to the nearest 0.25 bushels was converted to kg by using a conversion factor of 19 kg (42 lbs)/bushel. 4Suckers are a disadvantage because they serve as a source of infestation and must be removed. | ||||
| Table 5. 1998 Results -- NC-140 1994 Apple Semi-dwarf Rootstock Planting.1 | |||||
| Rootstock2 | Cumulative Yield per Live Tree (lb) | 1998 Yield3 (lb/tree) | Fruit Size (oz/fruit) | Truck Cirumference 10/98 (inches) | Number of Rootsuckers |
| M.26 EMLA | 138.9 | 48.5 | 4.8 | 7.0 | 0 |
| V.2 | 116.8 | 44.1 | 5.6 | 8.0 | 4 |
| CG.30 | 114.6 | 41.9 | 5.6 | 8.3 | 15 |
| B.9 | 68.3 | 28.7 | 5.4 | 5.4 | 0 |
| CG.11 | 26.5 | 4.4 | 4.7 | 11.9 | 9 |
| CG.13 | 22.0 | 4.4 | 5.4 | 12.2 | 15 |
| Mean | 68.3 | 24.3 | 5.4 | 9.2 | 9 |
| LSD (.05) | 37.5 | 15.4 | .7 | 1.2 | 13 |
| 1University of Kentucky, Research & Education Center, Princeton, KY. 2Arranged by cumulative yield in descending order. There is usually a direct correlation with trunk circumference and yield. 3Yield is the sum of picked and dropped fruit. Dropped fruit averaged less than 0.2 kg/tree for all rootstocks (LSD = 0.3). | |||||
| Table 6. 1998 Results -- NC-140 1990 Plum Planting.1 | |||||
| Rootstock2 | Cumulative Yield per Live Tree (lb) | 1998 Yield3 (lb/tree) | Average Wt/fruit (oz) | Number of Root-suckers | Trunk Circumference (inches) |
| Lovell Sdlg. | 198.4 | 11.0 | 2.0 | 1 | 16.0 |
| St. Julian A | 185.2 | 4.4 | 2.2 | 5 | 15.0 |
| Myrobolan Sdlg. | 180.8 | 4.4 | 2.0 | 49 | 15.5 |
| GF 31 | 178.6 | 4.4 | 2.3 | 7 | 15.6 |
| EMLA Pixie | 176.4 | 4.4 | 2.0 | 22 | 16.3 |
| Marianna 4001 | 174.2 | 2.2 | 2.2 | 14 | 17.7 |
| Marianna GF-8-1 | 165.3 | 0 | 2.3 | 59 | 18.3 |
| Myrobolan 29 C | 154.3 | 2.2 | 2.5 | 27 | 18.0 |
| Citation | 110.2 | 11.0 | 1.7 | 3 | 10.0 |
| Brompton | 108.0 | 4.4 | 1.9 | 8 | 11.4 |
| LSD (0.05) | 50.7 | 4.4 | 0.5 | 19 | 1.8 |
| 1University of Kentucky, Research and Education Center, Princeton, KY. 2Arranged by cumulative yield in descending order. 3Sum of both picked and drop fruit, but dropped fruit averaged less than 1 kg per tree. Yield was substantially reduced by late spring frosts. | |||||
| Table 7. 1998 Results -- 1994 NC-140 Peach Rootstock Planting.1 | |||||
| Rootstock2 | Cumulative Yield per Live Tree (lb) | 1998 Yield (lb/tree) | Trunk Circumference (inches) Spring | Average Fruit wt. (oz/fruit) | 90% Julian Bloom Date |
| Lovell | 227.1 | 178.6 | 14.9 | 2.8 | 90.7 |
| Stark's Redleaf | 165.3 | 123.5 | 13.5 | 2.4 | 89.3 |
| BY 520-8 | 149.9 | 123.5 | 13.6 | 2.8 | 88.8 |
| BY 520-9 | 147.7 | 108.0 | 13.8 | 3.0 | 88.0 |
| Montclair | 147.7 | 103.6 | 11.9 | 2.5 | 90.4 |
| Ta Tao 5 | 145.5 | 79.4 | 12.0 | 4.6 | 89.2 |
| Bailey | 138.9 | 83.8 | 11.9 | 3.5 | 90.1 |
| GF 305 | 134.5 | 108.0 | 12.0 | 2.4 | 90.6 |
| Tenn Natural | 134.5 | 92.6 | 12.2 | 3.2 | 90.3 |
| Higama | 132.2 | 97.0 | 10.0 | 2.3 | 90.0 |
| Rubira | 110.2 | 83.8 | 13.5 | 2.7 | 90.7 |
| Ishtara | 86.0 | 46.3 | 11.5 | 3.3 | 89.8 |
| Mean | 141.1 | 99.2 | 12.5 | 2.9 | 89.8 |
| LSD (.05) | 20 | 35.3 | 3.1 | 1.1 | 1.1 |
| 1University of Kentucky, Research & Education Center, Princeton, KY. 2Arranged by cumulative yield (kg/tree) in descending order. | |||||
Early production and optimal fruit size on vigorous sites are obtained when photosynthates are balanced properly between flower bud initiation and vegetative growth. Kentucky growers often have a problem with excessive vegetative growth or vigor, which greatly reduces the production that can be achieved from high-density apple plantings. Pruning and training are possibly the most important techniques used by fruit growers to maintain the proper balance between flower bud initiation and vegetative growth. Identification of effective pruning and training techniques for vigorous sites is required for continued expansion of apple production in Kentucky. The University of Kentucky College of Agriculture and the Kentucky State Horticultural Society have each made a long-term commitment to help meet this need. For this reason, research was initiated to determine the training and pruning practices needed to obtain early production and optimal fruit size from trees trained to either the slender spindle or the French axe system on vigorous sites.
One hundred eighty trees of Golden Delicious on M.9 rootstock were set out in May 1997 in a randomized complete-block design with eight treatment combinations (5 rows, 32 trees/row) and trained according to the treatment protocol outlined in Table 1. Tree spacing is 8 ft apart within rows 16.4 ft apart. Trunk circumference averaged 2 ft at planting and did not vary significantly among rootstocks. A trellis was constructed, and trickle irrigation was installed. Soil management is a 6.5 ft herbicide strip with mowed sod alleyways. Trees are fertilized and sprayed according to local recommendations (1,2). Yield (beginning with 1998 yield), trunk circumference, and maturity indices, such as soluble solids and flesh pressure, are measured annually.
Trunk circumference and average fruit weight did not vary significantly in the analysis of variance, but yield was significantly affected by pruning level (Table 2). Since this season’s fruit was left on the tree for purely training purposes, yield differences were probably more of a consequence of tree training procedures than of tree physiology. All trees are currently alive. During 1998, more than half the total time spent training the trees was spent during the first five weeks (Fig.1). In fact, there was more than a 50% reduction in time needed to train each tree from the third through fifth week than was needed during the first two weeks. About 60 seconds per week was needed to train each tree during the first five weeks, but only 40 seconds per week was needed in the 6th through the 12th week.
This planting, along with other plantings, is regularly used as a demonstration plot for visiting apple growers, Extension personnel, and research scientists. The research data collected in these trials will help to establish base-line production methods and economic bases for the various orchard system/rootstock combinations which can be later utilized by orchardists in Kentucky.
| Table 1. UKREC 1997 Apple Training Study -- Pruning/Training Treatments. | |||||||
| System | Pruning Interval Level in Wks | Headed at Planting | Angle1 | Limbs2 | Leader3 | Color Code | |
| French Axe | Light | 1 | No | 45 | No | D | Black/blue |
| French Axe | Moderate | 2 | 12-16 in. | 45-60 | Yes | C&D | Black/yellow |
| French Axe | Moderate | 1 | 12-16 in. | 45-60 | Yes | D | Black/green |
| French Axe | Heavy | 1 | 8-12 in. | 60-90 | Yes | D | Black/red |
| Slender Spindle | Light | 1 | No | 45 | No | A | White/blue |
| Slender Spindle | Moderate | 2 | 14-20 in. | 45-60 | Yes | B | White/yellow |
| Slender Spindle | Moderate | 1 | 14-20 in. | 45-60 | Yes | B | White/green |
| Slender Spindle | Heavy | 1 | 10-14 in. | 60-80 | Yes | C | White/red |
| 1Angle limbs are to be positioned. 2French Axe -- completely remove overly vigorous branches with narrow angles when 3 to 6 inches long. Slender Spindle -- completely remove branches that compete with leader. 3Leader management for 1999: A = weak leader renewal and new leader headed at 12 inches. B = bend leader at 60 angle, alternating direction with every 18" of new growth. C = leader bagged 1 month prior to bud break and bag removed at appropriate time. D = leader bent to horizontal, alternating direction after buds break on top side. | |||||||
| Table 2. 1998 Training Results -- KSHS-1998 Apple Training Planting.1 | |||||
| Pruning Level2 -- Interval in Wks | Trunk Circumference (inches) | Yield Per Tree (lb) | Average Fruit Wt (oz) | Minutes Per 10 Trees | |
| 19973 | 19984 | ||||
| Light - 1 | 4.0 | 1.3 | 10.7 | 122 | 102 |
| Moderate - 2 | 4.1 | 2.0 | 9.8 | 96 | 86 |
| Moderate - 1 | 4.1 | 2.4 | 9.2 | 114 | 111 |
| Heavy - 1 | 3.9 | 0.2 | 13.4 | 119 | 120 |
| Mean | 4.0 | 1.5 | 10.2 | 113 | 103 |
| LSD (0.05) | .3 | 0.9 | 3.7 | NA | NA |
| 1University of Kentucky, Research and Education Center, Princeton, KY. 2As described in Table 1. 3For 14 weeks. 4For 12 weeks. | |||||
Figure 1. Time Required in 1998 to Train Trees According to 4 Protocols.
Apples in Kentucky are subject to many important diseases. Among the most difficult diseases to manage in the summer are sooty blotch and flyspeck, because it is not known what time of the summer these diseases begin their fruit infections. A physiological disease, cork spot, also arises in the summer and requires management in the orchard. Sooty blotch is caused by a complex of several fungi formerly attributed to Gloedes pomigena, flyspeck is caused by the fungus Zygophiala jamaicensis, and cork spot is caused by calcium and/or boron deficiencies.
We knew from previous experiments (1-10) that little or no sooty blotch and flyspeck (SB and FS) developed on apples exposed to approximately 175 or fewer accumulated leaf wetness hours (LWH) after first cover and that disease levels increase with LWH greater than 175. The purpose of this experiment was to determine when these diseases occur by protecting susceptible fruits with multi-layer fruit bags at various times.
The experiment was conducted in a row of a block of 10-yr-old apple trees (Malus x domestica ‘York’) at Browning Orchard near Flemingsburg, Kentucky. The row was approximately 150 ft east of an adjacent woods. Early season disease management was done by the grower using an air-blast sprayer. All trees were sprayed at labeled rates with Manzate 200 80W (12 oz/100 gal) at pink and on May 21, which fell between petal fall and first cover.
Each experimental treatment consisted of applying multi-layer fruit bags (Kobayashi Bag Mfg. Co., Ltd. of Japan, available from Applecorps, 700 13th St. N.E., East Wenatchee, WA 98802-4523, USA) to 15 fruits (replications), divided among six trees (2-3 fruits/tree). All treatments were applied among the same six trees. Bags were applied according to manufacturer’s instructions and were randomly distributed between the tops and bottoms of trees.
For each treatment, fruits remained covered for a different period of the growing season (Table 1). The first treatments were made June 10, when fruits were about 1 inch in diameter. Succeeding bag application treatments were begun every two weeks thereafter. Fruits with bags removed prior to harvest were identified by tying surveyor tape around the fruit spurs; each treatment was assigned one tape color. Leaf wetness was detected and recorded electronically using an Envirocaster (Neogen, Lansing MI) weather monitor, starting at first cover (May 24).
All fruits in the experiment were harvested on October 8 and placed in cold storage with bagged fruits kept in their bags. Fruits were evaluated for SB and FS and cork spot on October 14. SB & FS severity was assessed by estimating the percentage of total fruit surface covered with the causal fungi. Cork spot severity was assessed by counting any sunken, dark spots on the fruit surfaces resembling typical cork spots. Representative spots were dissected to confirm the symptoms of this disorder. Treatments were evaluated for SB and FS and cork spot control by averaging the respective disease severities for all fruits in each treatment, followed by statistical analysis.
SB and FS symptoms were first noticed on July 7, when approximately 222 LWH had accumulated. June and August had more than average rain; July and September were dry. There was no obvious predominance of either SB or FS in any treatment. Compared with previous tests (2-10), disease pressure appeared to be light based on the low SB and FS severity on the control fruits. SB and FS was significantly reduced when fruits were bagged for three months or longer. Based on 4- to 5-week bag coverage, the most critical times to cover fruit to reduce SB and FS were July and August. In 1996, only treatments in which fruits were covered for all, or the last half of, July produced disease severity levels of 5% or less (3). Maximum cork spot reductions occurred when fruits were covered during August.
There was a significant positive correlation (r = 0.85) between SB and FS severity and total LWH to which fruit were exposed between first cover and September 10. The mean SB and FS severity for fruit covered from July 22 to October 8 was significantly greater than for fruit covered from July 7 to October 8, even though only seven hours of rain were recorded between July 7 and July 22. This observation suggests that another critical factor besides wetness contributed to SB and FS development in mid-July or that bags prevented SB and FS inocula from reaching the fruit in mid-July.
| Table 1. Effect of time of coverage by fruit bags on disease severity. | ||||
| Period of fruit coverage | Number of days fruits in bags | Number of hours of wetness between May 24 and September 10 while fruit were not covered | Sooty blotch and fly speck severity 1 | Cork spot severity 2 |
| Variable duration of coverage with fruit bags | ||||
| control - no bag | 0 | 341 | 1.39 cd3 | 1.54 c |
| June 10 - July 22 | 42 | 210 | 1.00 bc | 0.78 ab |
| June 10 - August 6 | 57 | 195 | 0.77 b | 0.54 ab |
| June 10 - August 24 | 75 | 129 | 0.36 a | 0.64 ab |
| June 10 - September 10 | 92 | 97 | 0.18 a | 0.36 ab |
| June 10 - September 22 | 104 | 97 | 0.25 a | 0.25 a |
| June 10 - October 8 | 120 | 97 | 0.00 a | 0.15 a |
| June 24 - October 8 | 106 | 170 | 0.13 a | 0.00 a |
| July 7 - October 8 | 93 | 222 | 0.20 a | 0.00 a |
| July 22 - October 8 | 78 | 229 | 0.89 b | 0.11 a |
| August 6 - October 8 | 63 | 244 | 1.00 bc | 0.63 ab |
| August 24 - October 8 | 45 | 309 | 1.38 cd | 0.25 a |
| Four to five weeks duration of coverage with fruit bags | ||||
| June 10 - July 74 | 27 | 217 | 1.11 bc | 0.78 ab |
| July 7 - August 6 | 30 | 319 | 0.86 b | 1.14 bc |
| July 22 - August 24 | 33 | 261 | 0.86 b | 0.29 a |
| August 6 - September 10 | 35 | 244 | 0.88 b | 0.25 a |
| August 24 - September 22 | 29 | 309 | 1.00 bc | 0.75 ab |
| September 10 - October 8 | 28 | 341 | 1.65 d | 0.77 ab |
| 1 Rating: 0 = no SB or FS; 1 = trace - 5%; 2 = 6 - 25% of fruit surface affected with SB & FS. 2 Rating: 0 = no cork spot; 1 = 1-2 cork spots. 3 Means in a column followed by the same letter are not significantly different (DMRT, P=0.05). 4 There was no mid-June treatment. | ||||
