Organic Control of Fungus in Vineyards, Eliminating Chemical Sprays

Organic Control of Fungus in Vineyards, Eliminating Chemical Sprays

Summary

WORK ACTIVITIES
This project is an attempt to organically grow grapevines in the high-pressure pest region of the Ohio River Valley. As noted in the project proposal there are many important reasons for growers to try alternative means for pest control that minimize and possibly eliminate the use of chemical treatments. After only one growing season it is understandable that unanimous skepticism remains amongst experienced grapevine growers. On the other hand there is every reason to believe this project should succeed given the preliminary results obtained this year (2007). The second growing season (2008) should be determinate if it includes the normal abundant rainfall, fog, and pest pressures common to the region.

As soon as funding was approved (spring 2007), clearing of trees and brush commenced on a one-quarter acre test plot, previously untreated in any way. This test plot will serve for future experiments even as the present project continues for its second and final season in 2008. Mature trees provide a wind buffer surrounding the test plot on three sides. This woodland also hosts abundant wildlife, fungi, and insects, some beneficial, but mostly harmful to vines. Another threat to the success of this project is the frequent fog from the Ohio River along with abundant rainfall, both of which are highly conducive to fungal growth. All geographical regions may have particular advantages and disadvantages for vine growing, and indeed the challenges faced by growers in the Ohio River Valley Region are legion, deeming this area a stringent test bed for experimentation. If grapevines can thrive in this environment (by any means) without the use of chemicals, it is believed that they can be productive almost anywhere without resorting to chemical sprays.

After clearing of trees and brush, terracing the steeply sloped (22-33%) ground began. It was soon apparent that the difficulty of this task was grossly underestimated, so a professional excavator was hired to complete the job. In spite of the high cost of terracing, the excavator was retained to build an access road which helped clear a path for erection of a wildlife fence.

Late spring planting instead of being a drawback was a great boon because the unseasonable 2007 freeze was thereby avoided. All vineyards (and orchards) in this area experienced considerable damage, and crop loss was significant. One new vineyard nearby will have to be completely replanted at great cost. While not yet tested, it is believed that if this project had been far enough along so that the test vines were enclosed within the plastic sheeting during the freeze, they would have survived. (Of course the unprotected control vines might have died and thereby derailed the project!)

Planting for the project could not be delayed long enough to complete the wildlife fence, and as a consequence significant deer pressure resulted in new growth being eaten wherever it penetrated the netting which covered the vines. While this continued to be a persistent problem throughout the growing season, the vines showed an abundant first-year growth of canes and foliage. Having plenty to do already, building the trellis system necessary to begin the experiment was undertaken in conjunction with fencing and staking of the vines. Yet given all these difficulties there was not one day of discouragement, and the entire family along with participating neighbors shared a truly remarkable experience!

As described in the proposal, plastic sheeting was draped over the top trellis wire and gathered together near the ground using clothes pins. On partially cloudy and on sunny days the temperature within the greenhouse-like tent was always measured to be 4-12 degrees greater than the ambient, and the enclosed vines thrived. Interestingly, as pupae emerged from the soil and munched on the leaves of both the control and test vines, it was observed that more damage was done to the lower leaves within the green-tent which was opposite the greater damage seen on the upper leaves of the control vines. While insect effects are not part of the project, this finding suggests that the worms did not like the higher temperatures of the green-tent. When the pupae metamorphosed into moths, those on control plants were able to freely lay eggs throughout the unprotected rows of the vineyard, whereas those moths in the test rows remained trapped within the enshrouding plastic sheeting. This made it easier for the spider population to prey on the trapped moths, and it was noted that the spider population was much greater within the green-tent environment. However it is unclear whether more spiders were present because of the warmth, the greater food supply, or both.

An early outbreak of downy mildew raised the excitement level as the project was now really underway. Would the green-tent test plants react differently than the controls? One possibility was that the closed environment around the test vines would enhance the growth of mildew. The hoped-for outcome was that the continual movement of sun-heated air rising from ground level to passively vent at the top of the plastic covered trellis would prevent the propagation of spores. At first we were surprised to see both effects until it became obvious that air movement was insufficient in some areas (including one end) of the green-tent. What to do? The forced-air system was not yet built. The solution was to use a gas-powered leaf blower temporarily duct-taped to one end of the green-tent. Several gas tank fills later the blower idea was abandoned and at first considered a failure. But when the vines were checked before nightfall, it was apparent that the downy mildew growth was arrested within the green-tent compared to the increased growth on the vines of adjacent rows. The following day three of us independently measured the per cent coverage of mildew growth on the leaves of test and control vines. No two observers’ measurements agreed. It was time to rethink where we stood, but the sun was too hot to make that possible. Retreating to shade and refreshments it became clear that data collection was being influenced by knowing which vines were in the test group and which were controls. It was decided to use a digital camera to take photos of selected leaves. The photos could be transferred to a computer and randomly arranged by the photographer for another person to assess the amount of mildew coverage on each leaf. Before this could take place, the unexpected summer drought began. At the time, no one knew that this would be a record-setting summer of high temperatures and drought the likes of which had never been experienced by most Ohio River Valley farmers. Before any pictures could be taken, the sunlight and heat killed-off the downy mildew we had seen in the previous two days. It did not reappear on either control or test plants throughout the remainder of the growing season.

Work continued throughout the very dry hot summer, vine-tending, trellis and fence building, hand-weeding, and planting a variety of ground covers searching for an erosion-control solution for the rains that would eventually come. Insect damage was noted to be greater on some vines than others, but the damage to leaves did not seem significant given the abundant growth. The deer continued to munch on exposed leaves that grew through the netting on control vines, but they did not bother the plants within the plastic green-tent.

Another problem to solve arose with winds gusting to 12 knots. The clothes pins could not hold the plastic sheeting which looked like a giant sail as it lifted off the trellis. The sheeting was reinstalled with metal binder clips, but the next series of high winds were too much even for these much stronger fasteners. Clearly enough rocks or dirt piled onto the edges of the plastic would hold, but there would be no convenient way to tend the vines. The solution to this problem (so far anyway) was to partially melt the edges of the plastic sheeting so that a roughened area was formed for the binder clips to better grab hold. Several bouts of severe weather have yet to send the plastic sheeting flying.

Now that the usual rains have returned (post harvest time), there is black rot everywhere in the vineyard on the control plants. The vines within the green-tent however show very little infection, less than a dozen leaves out of thousands. These few infected leaves were easily removed to prevent the spread of the germinating spores. After leaf fall, it is planned to remove all leaves from the vineyard for disposal well away from the test plot. This widespread outbreak of black rot indicates that there will be a serious problem in normal rainfall growing seasons. That only very little rot was found within the green-tent (so far) is indeed very exciting.

Another indication that this was an odd weather season is that no powdery mildew outbreaks occurred even on the lilacs which are always covered with this fungus. The final project year (2008) should prove more decisive in evaluating the efficacy of the green-tent system assuming the usual rainfall will occur.

NCR SARE grant funding was especially welcome because actual expenditures far exceeded proposal estimates.

Budgeted expenses for next year include additional outreach (presentations, web site publications) and data collection.

RESULTS
•Plastic sheeting draped over the top trellis wires of grapevine rows can successfully form greenhouse-like tents secured against high winds using metal binding clips affixed to roughened (partially-melted) edges at ground level.
•Standard building supply 6-mil plastic sheeting allows plenty of sunshine for vine growth, but whereas it is tough enough to prevent rips and holes, it is considered by some workers to be too cumbersome to repeatedly lift, temporarily secure at the top of the trellis while vine-tending, and reposition and refasten at the bottom of the curtain before moving on to the next section.
•Temperatures within the green-tent are 4-12 degrees warmer than ambient on partially cloudy and sunny days.
•Warmer temperatures appear to favorably encourage beneficial spiders while limiting the spread of (moth) pupae from the newer leaves and tendrils found at the top of the canopy.
•Preliminary indications are that forced-air drying of downy mildew infected plants is effective in controlling the spread of this fungus. A full growing season of data collection will be needed for verification.
•For unbiased data evaluation it is mandatory that reviewers not know from which plots (test or control) the plant material was selected. It is hoped that pictures taken of plots, individual vines, and infected leaves will prove useful for making unbiased measurements. (Of course it would be best if the photographer were not knowledgeable of which plants were in which group.)
•Deer netting is insufficient for protecting new growth of vines from being eaten wherever it penetrates the mesh, whereas plastic sheeting completely prevents access by foraging deer.
•Early indications are that black rot spreading is retarded in the green-tent environment. If this finding proves valid, then it will be interesting to test if it is the barrier itself that is being effective in preventing the penetration by spores, or if it is the hotter, dryer environment that is the cause.
•Completely unplanned is the finding that drought conditions (lack of moisture in the case of downy mildew and black rot, and high temperatures in the case of powdery mildew) are not conducive to fungal growth in vineyards. This was probably well known before the use of pesticides became prevalent in farming. Grape growers of the Ohio River Valley Region should certainly be encouraged to use fewer chemical treatments when these rare conditions occur.

WORK PLAN FOR 2008
Now that the one-quarter acre test plot is planted in rows of protected (green-tent test group) and unprotected (control group) grapevines, it is necessary to collect and evaluate sufficient data to report on the relative efficacy of the green-tent environment in retarding and hopefully preventing fungal growth. This should be possible given a normal (drought-free) growing season.

It is expected that the great reduction in project labor will allow sufficient time for new experiments to be conducted in parallel.

OUTREACH
In addition to the planned site visits, word of mouth sent several dozen visitors to see the project. Their comments were interesting if not always positive!

It is expected that the number of casual visitors will significantly increase after photos and documentation are published on the Internet. All will be welcomed.

If the project is successful, then a field day will be held and site tours given. Even an unsuccessful outcome will be submitted for publication by one of our student helpers.