Results of this study clearly demonstrate that properly managed peach orchard ground cover reduces certain insect pest pressure and subsequent damage to the crop. Peach growers participating in this project had 3 times less damage caused by tarnished plant bug feeding in orchard blocks with managed sod ground covers compared with fruit grown with weedy ground covers or disked orchard floors. Likewise, while testing the suitability of various ground covers and management practices for use in integrated peach production, we collected 3 times more tarnished plant bugs from weedy orchard floors compared with the number found in sod ground covers. Tarnished plant bug levels were also lower in ground covers where herbicides were used to remove broad leaf weeds and alternate host plants of this pest. This project also showed that some ground covers can effectively reduce the population of certain nematodes but simultaneously have the potential to increase others. Certain peach diseases including brown rot, cytospora canker, and bacterial spot were not influenced by different ground cover management practices.
1. Demonstrate how orchard ground cover management affects arthropod abundance and damage to peaches.
2. Demonstrate suitability of selected ground covers for use in integrated crop production strategies for peaches.
3. Determine how plant parasitic nematodes are affected by ground cover type and management strategies.
4. Determine if ground cover management affects incidence of selected peach diseases.
We conducted several studies to demonstrate and investigate how orchard ground cover management affects certain peach pest levels. For the first objective, we used four commercial peach blocks to demonstrate how sod ground cover can be used to reduce insect pest damage to peaches. Each block was at least 12 acres in size. Each blocks was divided into 3 plots then assigned 1 treatment per plot. The 3 treatments consisted of (1) hard fescue sod (variety SR-3100) established in the drive rows, (2) naturalized vegetation (weeds) maintained in the drive rows, and (3) disked drive rows. The sod and weedy drive rows were periodically mowed while the disked blocks were cultivated less frequently to kill emerged weeds. Each of the 3 treatments at a grower site were sprayed with the same arthropod and disease sprays so that any differences in observed pest levels or damage could be attributed to the ground cover treatment. Harvest samples were collected at 2 of the 4 sites; the other 2 sites had limited fruit numbers because of a localized freeze during bloom. The harvested fruit was evaluated for damage.
Plant parasitic nematode samples were also evaluated from the 4 commercial sites described above in Objective 1. No differences in nematode population levels were observed 1 year after establishment of the ground cover treatments but population levels were low for the duration of the experiment. Nematode samples collected from the 8 different ground cover treatments described for Objective 2 indicated that nematode populations increased in all treatments except where the soil was kept relatively free of vegetation by either disking or herbicides (Figure 4). These 2 bare soil treatments could not sustain plant parasitic nematodes because of the lack of a continual source of vegetation.
In the past it did not matter which nematode needed to be controlled because nematicides were effective against all nematodes. However, results of these tests indicate that the effective use of biologically based controls for nematode management will require a greater understanding of the specific problems facing individual growers. These data suggest that selected ground covers can effectively reduce populations of certain nematodes but may simultaneously have the potential to increase others. For example, â€˜conservation mixâ€™ may effectively suppress root-knot nematodes but increase the number of dagger nematodes.
This â€œtrade-offâ€? does not necessarily present problems since plant-parasitic nematodes are not uniformly distributed and an increase in other nematodes may not occur. However, to effectively utilize these biologically based pest management techniques it will require that fruit growers become better educated about the specific nematode, insect and disease problems that they are attempting to control. Furthermore, there will be an increased demand for diagnostic services for accurate identification of these pests.
The effect of ground cover management on the incidence of peach diseases was investigated in Objective 4. Treatment trees in the commercial orchards were assessed for disease approximately 5-7 days before harvest. In each plot, five trees were selected per treatment. A total of 20 fruit were selected from around the periphery of each tree providing 100 fruit per treatment. Each fruit was rated for incidence of bacterial spot, brown rot, rusty spot, and scab. Results were expressed as percent of fruit infected for each disease. Shoots on which the fruit were attached were also examined for presence of blossom blight canker.
A considerable amount of bacterial spot infection was observed in both orchards and across all treatments. At one site, fruit disease incidence ranged from 44% to 46%, while the level of disease ranged from 28% to 33% infected fruit at the other site. Although disease incidence was high, the level of severity was low with most fruit showing 10 or fewer lesions.
The incidence of rusty spot was low, ranging from 1% to 8% of the fruit infected and most fruit had only one or two visible spots. No treatment effects were observed. No blossom blight canker, fruit brown rot, or fruit scab were observed in any of the treatments in either orchard.
None of the ground cover treatments appeared to have any effect on the level of disease. This may be due to one of two reasons or both. First, all of the treatment blocks received regular applications of fungicides and bactericides. These sprays probably provided a much greater effect on disease level than the ground cover treatments. Thus, any differences between the treatments may have been diminished or totally eliminated by the sprays.
The second and perhaps more important reason for lack of treatment effect relates to location of pathogen inoculum and method of dispersal. For all diseases surveyed in this study, the overwintering inoculum is primarily located within the tree canopy or outside the orchard itself. Consequently, inoculum dispersal is not influenced by the ground cover treatment. Brown rot cankers and mummies, bacterial spot cankers, and scab twig lesions are all found on above-ground tree shoots. Rusty spot inoculum consists of apple mildew conidia blown in from nearby apple orchards.
The only possible orchard disease inoculum that may be influenced by ground cover management is fallen brown rot mummies. However, even in the absence of this inoculum source, prolific sporulation on cankers and aerial mummies should be sufficient for generating significant disease pressure. One aerial mummy or canker can generate millions of spores, all capable of initiating an infection.
Results from this project have been widely disseminated at three regional pest management conferences whose audience consisted of research and extension personnel, industry representatives, and fruit growers. The meetings where project results and implications were presented included the 59th Annual Meeting of the New England, New York, Canadian Fruit Pest Management Workshop; the Cumberland-Shenandoah Fruit Workers Conference (includes published abstract); and the New Jersey Agribusiness Association Annual Conference. The results from this project will also be presented during a Symposium at the Eastern Branch Meeting of the Entomological Society of America during March, 1998. At least 100 growers will be presented with these results at grower meetings in NJ, during late winter, 1998. These results will also be disseminated through newsletter articles. A fact sheet describing how peach orchardists can reduce pest damage with ground cover management is being prepared and should be available for distribution during the summer of 1998. We will continue this project an additional year and will publish our findings as 3-4 journal articles (2 articles in refereed journals and 1-2 as trade journal articles).
Impacts of Results/Outcomes
We expect that there will be positive impacts on overall farm productivity, the environment, and farm profits as growers adopt and successfully implement good ground cover management in their orchards. The benefits growers should see in the short-term are reduced damage from certain pests, reductions in pesticide applications because of lower pest levels, and increased profits resulting in better fruit packout (less damaged fruit) and reduced pesticide input. Long-term benefits include reduced soil erosion because sod holds soil in place and increased soil organic matter in sod versus disked areas. Other benefits include decreased costs and energy use because of reduced frequency of mowing slow growing hard fescue sods compared with typical orchard grass, reduced insecticide-related bee kills because the lack of white clover in well managed orchard ground covers should reduce bee foraging in orchards after bloom, and potentially less frost damage to crops grown with sod versus disked row middles because orchard temperatures during frosts are frequently warmer with sod ground covers compared with temperatures found in disked areas.
We have already seen an impact in the three commercial peach orchards used in this study. Two of the three grower-cooperators established sod in newly planted orchards because of the information gleaned from reading and discussing the project proposal. The third grower already has most of his orchard in sod but now recognizes the importance of keeping weeds from flowering in his orchard to reduce insect pressure.
We have developed or will re-emphasize several recommendations to growers based upon findings from this study. These include:
â€¢ Minimize insect pest problems and soil erosion by planting sod in drive rows instead of disking;
â€¢ Manage orchard sod to minimize insect and nematode pest pressure;
â€¢ Remove established broad leaf weeds and clover from the orchard;
â€¢ Do not mow or disk if insects are present in the ground cover to prevent them from dispersing up into the trees;
â€¢ Do not plant legumes, especially white clover, during rotations to rest the soil before replanting peaches. This should reduce plant-parasitic nematode populations and plant virus inoculum.
Areas needing additional study
Several areas of additional research have been identified which, if conducted, will further our knowledge regarding orchard ground cover management. First, screening additional ground covers for nematode, plant virus, and insect resistance may result in the discovery of better ground covers. Secondly, because good ground cover management can reduce pest pressure, determine if this can be translated into reductions in pesticide use. Finally, this research should be expanded to other orchard crops because several key pests that attack peach also are pests of apple, pear, cherry, and plums.