2015 Pre-Bloom Disease Management Review
By: Bryan Hed
Well spring is here, and with a new season of grape production soon upon us, a review of pre-bloom disease management topics is in order. In addition to adjusting and carefully calibrating sprayers, take some time now, before bud-break, to acquaint yourself with the NEWA website (Network for Environment and Weather Applications) found at http://newa.cornell.edu . This website gives you easy access to a wealth of weather and pest forecast information from an extensive network of weather stations positioned all over the Northeast…and it’s free. When you first access the site, you’ll see a map of the northeastern U.S. You can use your cursor to navigate the map and click on the weather station nearest you (denoted by a leaf/rain drop icon) to tap into daily and hourly weather (temperature, rainfall, leaf wetness duration, wind speed, etc) near your vineyard or any location you choose (hmm, we had 21 below zero on February 16, I wonder how badly southern PA was hit…). Clicking on ‘grapes’ under ‘crop pages’ will give you access to disease forecasting models for the ‘big four’ like Phomopsis cane and leaf spot, black rot, and powdery and downy mildew. You can also access the grape berry moth degree day model that will help to take a lot of the guesswork out of timing your berry moth insecticide sprays later this year. Each model forecast is accompanied with disease management messages and explanations. For example, at our present stage of development, ‘dormant’, the website has this to add about Phomopsis control: ‘Dead and diseased canes, arms, and pruning stubs should be pruned out to reduce inoculum. Dead canes and stubs can produce extremely high levels of Phomopsis spores over several years. In particular, growers seeking to minimize fungicide use should pay strict attention to the removal of infected wood from within the canopy’. This is a great way to educate yourself on the challenges ahead as we strive to make the most effective and cost worthy decisions in our efforts to grow healthy grapes. Check it out!
For many of us, Phomopsis cane and leaf spot will be the first fungal disease we encounter during the early shoot growth stages in late April (?) and May. I have included several pictures below to help reacquaint you with symptoms on shoots, canes, and leaves. This fungus is often a threat during those long rain periods in May. Young shoots are capable of becoming infected as soon as they emerge and inflorescences ($) can be impacted by this pathogen around the 3-6” shoot stage (basically when they become visible). Infections on newly emerged inflorescences can literally ‘bite off’ whole sections of the cluster and reduce crop potential very early in the season. Early infections on flower stems can move into berries later in the season, during ripening, and cause fruit drop or even fruit rot (either way, you lose). So, If weather is wet at this stage (3-6” shoots), an application of mancozeb, ziram, or captan will limit these infections that can lead to early destruction of clusters or sections of clusters, fruit rot, and ultimately, reductions in yield. Work by Wayne Wilcox has shown that this fungicide application can significantly increase yields and easily pay for itself (sprays at this time are generally pretty inexpensive). This spray can also protect against early shoot infections that become a source of inoculum (canes) in the following year. So, fungicide applications at the 3-6” shoot stage double as an insurance policy against crop loss in subsequent years.
For symptoms on wood (below), look for scabby lesions on the first 2-4 internodes of year-old canes (from last year’s infections in early May), and/or an abundance of old pruning stubs and older and dead wood.
Although the 1” shoot stage can be vulnerable to damage from this pathogen, the more critical stage is at 3-6” shoots, when more shoot, leaf, and cluster tissue is exposed and is highly susceptible (below).
Sprays for powdery mildew will likely be necessary at very early shoot growth stages for highly susceptible Vitis vinifera cultivars and/or where control of this disease was lacking the previous summer. Research at Cornell has shown that vineyards harboring high overwintering inoculum levels may require that control measures commence earlier the following season to avoid epidemic development and crop loss. A tenth of an inch of rain with temperatures above 50 F constitute a primary infection period for powdery mildew. Materials like sulfur, oils, Nutrol, and potassium bicarbonate materials may be good first choices for mildew at this stage. Keep in mind that you can’t mix sulfur and oils, or oils and captan (read the labels!). For juice grapes like Concord and Niagara, powdery mildew control is generally not a concern at this time.
For black rot, old fruit mummies and clusters (infected from the previous season) are prime sources of inoculum in spring and early summer, and thorough removal of all this material from the trellis during dormant pruning is essential to maintaining good control of this disease. Once on the ground, mummies can be buried with cultivation or mulch, reducing or eliminating their capacity to fuel new infections in spring. A fungicide application for black rot may not be necessary at these early shoot stages if good control of this disease was achieved the previous year and conscientious trellis sanitation has been implemented. On the other hand, inoculations we performed at these early shoot growth stages (simulating wet weather and an overwintering inoculum source in the trellis) can produce leaf and shoot infections in the cluster zone, that go on to release spores during early berry development stages, and that result in fruit infection and crop loss. An application of mancozeb, ziram, or captan for Phomopsis will also provide control of early black rot infections.
At about 10-12” shoot growth or the 5-6 leaf stage, a fungicide application at this time will limit infections of Phomopsis on shoots, and cluster and berry stems, especially in vineyards at high risk. Black rot control may not be critical for juice grapes at this time if excellent control of this disease was maintained in previous years and conditions are dry. However, it would be advisable to apply a fungicide for black rot if conditions are wet and warm, especially to Vitis vinifera and susceptible hybrids. As mentioned earlier, black rot leaf and shoot infections at this time can increase inoculum levels in the cluster zone, making black rot control more problematic during the fruit protection period (after capfall). If scouting reveals black rot lesions on leaves in the cluster zone, this is a great big red flag! Make sure your subsequent black rot sprays are effective and timely, especially during the fruit protection period. Downy mildew becomes a concern at this stage as well and fungicide sprays for this disease will be necessary for susceptible varieties, especially if conditions are wet. Mancozeb products offer one of the best control options for all three diseases. Ziram is a little weaker on downy mildew, and Captan a little weak on black rot, but these may also be an option if these diseases are not a priority at this time.
Powdery mildew is less of a concern at this time for juice grapes than for wine grapes, but may be necessary if susceptibility and risk of disease is high, especially for growers of Vitis vinifera and sensitive hybrid wine grapes. Sulfur is an inexpensive option for powdery on non-sensitive varieties. The sterol inhibitor fungicides may also be good choices at this time, providing they are still effective in your vineyard. Note that the sterol inhibitor and strobilurin fungicides have been in use for many years in Pennsylvania vineyards and are considered at high risk for the development of resistance by the powdery mildew fungus, that is, they may not be as effective as they used to be, or are ineffective. If you suspect powdery mildew resistance to these materials in your vineyard, either apply them in a tank mix with another active ingredient for mildew (like sulfur) or discontinue their use and use an alternative active ingredient. This is even more critical for the next two fungicide application timings; the immediate pre-bloom/first post bloom sprays.
Immediate pre bloom/first post bloom fungicide application.
These next two sprays – immediate pre bloom (just before the beginning of capfall) and first post bloom – are critical for every vineyard, every year, for control of every disease!!! Young fruit of every variety are most susceptible to all the major diseases (Phomopsis fruit rot, black rot, downy and powdery mildew) during the period from bloom to about 2-3 weeks after bloom. Apply your most effective materials (Strobies (if no resistance issues), Quintec (powdery only), Manzates/Ziram/Captan (for Phomopsis, black rot, downy mildew)). This is also the perfect time to consider some of the newer products like Vivando or Torino (for powdery mildew only), Revus Top (for powdery and downy mildew and black rot), Inspire Super (for powdery mildew and Botrytis), Luna Experience (wine grapes only, for powdery mildew, Botrytis, and black rot) and the newer downy mildew materials (listed below). Plan to apply for best coverage, every row, full rates, and shortest intervals (NEVER extend the interval between these sprays beyond 14 days).
Phosphorous acid products (aka phosphites, phosphonates) have become favorites for many growers as a means of controlling downy mildew. They are effective and ‘friendly’ to work with. However, if you use these materials at this time, be mindful that, although they are extremely rain-fast, they still provide only limited protection against new infections. Do not expect phosphorous acid sprays to provide more than 10 days of protection, especially under high disease pressure.
Relatively new downy mildew materials
- Revus; contains mandipropamid, registered in 08. Very effective on downy mildew in PA and NY trials.
- Presidio; fluopicolide, registered in 08. Very effective on downy mildew in PA and NY trials. Label requires that Presidio be applied as tank mix with another downy mildew fungicide.
- Reason 500 SC; fenamidone, which is a quinone outside inhibitor; same mode of action as strobies, but not technically a strobie. However, treat it as a strobie with respect to resistance management. Provided excellent control of downy mildew in Cornell trials.
- Quadris Top; azoxystrobin + difenoconozole; for downy and powdery mildew, black rot, and Phomopsis. New combination of current chemistries. Its use on grapes in the Lake Erie region will be greatly restricted: with azoxystrobin in the mix, this can’t be used in Erie county PA, and with difenoconazole in the mix, this can’t be used on Concord.
- Ranman; cyazofamid, a new chemistry for downy mildew. PA and NY trials show good to excellent efficacy against downy when applied alone and mixed with phosphorous acid.
- Zampro; ametoctradin + demethomorph. The newest of the new downy mildew materials; a combination material that is very effective on downy mildew.
A new material, Aprovia, may be available for 2015 (?), mainly for powdery mildew. Federal registration is anticipated in April of this year. This material is related chemically to Boscalid (found in Endura and Pristine) and Fluopyram (found in Luna Experience).
And finally, a short recap of some main points – in no particular order of importance – when planning your pre-bloom disease management programs…
- Overwintering inoculum control = maintaining a relatively clean vineyard through to harvest (in the previous year) and subsequently, thorough sanitation during dormant hand pruning activities.
- Good overwintering inoculum control will make seasonal disease control more forgiving (‘I can’t get a spray on because it won’t stop raining; good thing I controlled diseases well last year!!’); consider it an insurance policy. Your pre-bloom spray programs will also be more effective as they are applied to control a smaller initial pathogen population this year.
- Early spray programs are relatively inexpensive. If disease control was lacking last year, higher overwintering inoculum levels will require that you fire up your seasonal spray program earlier this year, especially if conditions are wet.
- The bloom and early post bloom periods are the most critical for protecting your crop ($) against all diseases; it is never cost effective to cut corners during those stages of crop development.
- Scout your vineyards and develop your skills at identifying diseases; know what it is you’re trying to control. Focus your scouting efforts in vineyards/vineyard areas where disease control has been most challenging (where you expect disease to show up first). Discovering disease in its earliest stages is key to controlling it, and you can’t discover it early if you don’t scout!
- Know your fungicides; their strengths and weaknesses, the specific diseases each material controls, and their rotational partners for resistance management.
- Read labels!
- Prepare yourself to make the most of the 2015 growing season with a run through the NEWA system.