Spring has sprung a leak. The negative effects so far range from a nuisance to some potentially significant yield reduction, along with increased costs in any case. What the future holds for the season is hard to determine at this point. It’s a little like baseball; there can be some interesting events early on, but how the season ends up is anybody’s guess.
Rainfall to date (for San Joaquin County) is almost the same as last year, being only slightly ahead at 23.1 inches for the north county and 15.4 inches forth the south county, south of Stockton. Those totals compare to 21.9 inches in 2005 for the North and (surprisingly) 17.1 inches for the South. The big differences are: last year March was very dry, temperatures were warm and winter weed cover was dramatically more expansive compared to weed growth this year. The immediate threat of flooding for some locations has been real, but the general concern continues to be that the wet cold weather increases costs of production with some real threat of crop loss, depending on the commodity.
An early bloom was drawn out to one of the longest in memory. The initial weather was good for earlier blooming varieties such as Nonpareil and Sonora, but they still suffered some frost damage. Since then the weather has been more like the Pacific Northwest for the bloom of later varieties such as Butte and Padre. So far anthracnose has been in check, while shot hole has been a little more obvious.
Continued protection may be needed in both cases as long as the rain keeps up. Be on the lookout for leaf lesions that might be sporulating Shot Hole. For Anthracnose the damage symptoms can be more dramatic with yellowing of leaves, immediate leaf loss, dieback of smaller shoots and a characteristic rust or orange colored gumming on any tissue. Fortunately there are many new materials becoming available that have broad spectrum control. Talk to a local PCA and/or check out the UC IPM Pest Management Guidelines at www.ipm.ucdavis.edu.
The Nonpareil crop looks better than last year, but not huge. Many of the other varieties look okay at this point, but the cold, wet weather has many people concerned about what the effect will be on the “June Drop.” A lot of the varieties have a wide range of nut development. Along with the poor growing conditions, both could make for a big crop of nuts before it is all over.
If the nut drop is high in a particular block, reducing the normal nitrogen application and putting some of that savings towards potassium might be a good idea, especially if potassium hasn’t been part of a normal program in the last few years. While leaf tissue analysis is not infallible, a good representative sample from each area of an orchard or block is good for detecting problems in productivity or tree growth over time.
As the season progresses keep an eye out for the lower limb dieback problem that has been popping up the last couple of years. There may be several factors involved, one of them being disease, but there is still no definitive answer as to what is going on. In the last year some hints have come to light as to the disease possibilities. The symptoms – smaller twigs and branches that quit growing and dieback a short distance with no obvious cankers or disease and seem limited to the lower third of the tree canopy-have been a puzzle, to say the least. There seems to be some indication that two fungal species, Phomopsis and/or Botryosphaeria, are often, but not always detected. (Farm Advisors) Roger Duncan, Brent Holtz, and (UC Plant Pathologist) Themis Micailides are investigating the problem.
For grapes there has been less of an immediate problem, as cold temperatures have put bud break behind by about two weeks for most varieties. Chardonnay and Grenache were only slightly behind normal, but shoot development has slowed to a crawl, setting up good conditions for powdery mildew, Phomopsis, and Botrytis shoot blight to become concerns. As in 1995 and 1998, downy mildew may make a return on sensitive varieties such as Barbera and Chenin blanc.
Most of the major varieties are not highly susceptible to Phomopsis, with the exceptions of Grenache and maybe Syrah. Wettable sulfur can be very effective, although there are several new materials and Captan is still available. Wettable sulfur after bud break can be a very effective and inexpensive choice for doubling up on an early start to powdery mildew control. Whatever the material of choice ends up being, a good powdery mildew program includes: some sulfur, rotation of materials between years, and complete coverage. Each component is important Sulfur does not control downy mildew.
Last year, I expected downy mildew problems, but it was dry enough at bud break, with enough drying in between storms until the end of the rainy period that it was not a concern
Downy mildew first made an appearance in the area during 1995 and reappeared in 1998. Although now established in California, downy mildew needs very wet and mild conditions to become a problem. Most of the vinifera varieties are fairly susceptible, but Barbera and Grenache seem to be especially so. Be on the lookout for downy white spots that turn brown and necrotic on the underside of leaves, with corresponding light yellow green patches on the top of the leaf. There are effective materials, but check with your PCA or the UC IPM Guidelines.
Botrytis shoot blight can be a problem if conditions stay cool and wet as in 1995 and 1998. Scattered shoots that wilt and de anywhere from just below the growing tip to more than halfway down, with some fuzzy gray mold at that point, or scattered clusters that wither in part or entirely, is most likely early Botrytis. Usually the number of affected shoots is very minimal and only becomes a real problem in years like 1995 and 1998. Syrah and Viognier seem to be very susceptible and clusters on Symphony have shown severe problems. Botrytis sprays can be helpful, but probably are not very cost effective, unless one of the other spring diseases is also in need of control.
Soil water availability is obviously high this year, maybe even more so than last year, as the heavy rains have been late. That may provide the potential for big canopy development, as last year, but whether that translates to a bigger than normal crop is hard to predict.
The probability is for a normal or below normal crop, but that depends on growing conditions. Although the 2005 crop was huge and late, the large canopies, mild conditions and long mild fall allowed most vines to recover well before leaf fall. In any case the vines usually don’t read the literature about what they should do.
Irrigation shouldn’t be a big concern for a while. The hope is that although spring- can be delayed, it can’t be denied (unless summer gets here first).