A Strawberry Multi-dimensional IPM Systems Comparison Demonstration 1997

Author: Joe Kovach, Dept. Entomology, Ohio Agricultural Research and Development Center, 1680 Madison Ave., Wooster, OH 44691-4096

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RESULTS AND DISCUSSION

Because there was very little clipper injury and only a few spittlebugs or mites were collected from the treatments, no specific data for these pests are presented. In addition, data are not presented for disease incidence because less than 1% of the berries were damaged at harvest by Botrytis and there was no difference between treated or untreated plots.

A summary of the yield assessments at the 5 harvest dates is presented in Table 1. About half of fruit was harvested in the three early picking dates and the remainder was picked in July (late). For economic analysis, the early picking was considered to be fresh marketed while the late picking was considered to be marketed for processing.

Table 2 shows the mean number of fruit, weight and fruit size for the three treatments.. According to published reports, the ribbon row system should outperform the matted row system in the first fruiting year, primarily because of an increase in row density per acre. However in this experiment, the treatments with the ribbon row system (IPM and ORG) produced significantly fewer and smaller berries per meter than the matted row system. On a per meter of row basis, the ribbon row systems produced about 45% of the fruit. This makes sense since the rows in this system were about half as wide as the matted rows. Although there were 20% more rows in the ribbon row system than in the matted row system, this increased row density was not large enough to compensate for the lower yield per meter.

Nutrient analysis showed that there was no difference in nutrients between treatments and all nutrients were within acceptable ranges for all treatments. Since nutrient levels were equal, the only other possible factor that may explain these differences was that planting into the killed rye had some effect on plant health. Although the strawberry plants appeared healthy, this rye cover crop may have had some unrecorded or unobserved impact on plant establishment or other physiological process, thus lowering yields.

Weed samples from each treatment plot were collected in June 1996 and at three times in 1997. These results are presented in Table 2. Weed control was good in all treatments in 1996 and there was no difference between treatments. In 1997, however weed control was the best in the CON treatment, with the control being marginal in the IPM plots and relatively poor in the ORG treatments particularly in the May sample. A high percent (>90%) of the weed biomass collected in this field were dandelions. Even though weeds were hand removed prior to bloom in all plots, the increased weed density found in the IPM and ORG plots may have been an additional factor why yields were reduced in these treatments.

Tarnished plant bug injury was substantial in all plots in 1997. Although plenty of TPB were collected in the alfalfa surrounding the plots, there was no difference in TPB numbers or fruit damage between subplots that were located next to the alfalfa and those in the center of the plots (P<0.05). Figure 1 shows the strawberry sampling results of TPB throughout the early season. A conservative threshold of 0.25 nymphs/cluster was used to begin the spray treatments. The one spray of malathion provided seasonal control of TPB whereas the multiple applications of Mycotrol did suppress the TPB populations compared to the untreated check but did not provide the same level of control as the malathion.

Figure 1. Mean number of tarnished plant bug nymphs per flower cluster in the different treatments. IPM plots were sprayed 3 times with Mycotrol (1 qt/A), Conventional plots were sprayed 1 time with Malathion (1qt/A).

Table 4 shows the percent strawberries damaged by tarnished plant bug at the early and late pickings. The one spray of malathion resulted in the fewest berries being damaged by TPB on the day neutrals and Earliglows. The 3 sprays of Mycotrol reduced the number of TPB damaged fruit in both pickings of these cultivars when compared to the check. The three vacuuming sessions also reduced the number of TPB damaged fruit, particularly in the late picking. Although the Mycotrol and the vacuuming did provide some level of control on the `Earliglow' and day neutrals, just planting `Honeoye' and doing nothing gave similar or better control.

The total number of damaged berries and the mean number of TPB nymphs in the unsprayed checks of `Honeoye' strawberries was significantly less than in the unsprayed `Earliglow' or day neutrals berries (Table 5). These results are similar to reports by other workers that `Honeoye' strawberries are resistant to TPB. It is not know whether this resistance is due to repellency (of adults or nymphs), antifeeding chemicals being present in the berries or some mechanical method of preventing seed damage (having thicker, tougher seeds). From our sampling results it appears that the resistance in this cultivar may be due to repellency and not due to the presence of some antifeeding chemical or other means because there were fewer nymphs present on `Honeoye' flower clusters than the other cultivars. Whether repellency affects the adults (fewer eggs laid), the eggs (fewer hatch) or the nymphs (some irritant is present and the nymphs move off the plant) is not clear. Although we do not know what the actual resistant mechanism may be, it is real and measurable.

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