We have been hearing rumors about a shortage of liquid mancozeb products. I spoke to a rep at UPL, the company that makes Manzate Max. The rep informed me that there is a global shortage of chlorothalonil, which has driven the demand for mancozeb way up from last year – creating somewhat of a shortage of those products too. They are rushing to catch up, and more products should be in the supply chain and on shelves soon.
Insects
This is the week for scale! Based on several samples, the female scale started producing eggs and crawlers just this week. If you have active scale spots (many are old dead areas), now is the time to use your spray to manage these insects. There is variability based on area and variety, but generally this weekend is the target. Bees are in, so be sure to spray at night.
Many growers report remarkably empty sweep nets this week. Generally, no counts or low counts of weevil, which is good given the bees are here. A few casebearer, in small numbers, have been found. Unless you find a lot (10-20), I would be hard pressed to spray an expensive Diazinon to control.
Remember, Altacor for fruitworm should not go on until 50% out of bloom or when you can find some berries that have sized up from pinheads. This is likely at least a week or two away. Super hybrids move fast with pinheads progressing to bigger fruit rapidly and the fruitworm will target these first with their eggs.
Weeds
Spot spraying concentrated Callisto solutions for poison ivy control is the one of the best tools we have for managing this difficult weed, and the first application can go out anytime now. Our research showed that by mid-June, PI has invested stored resources on growing full-sized leaves, and now it the time to knock it back with a spot treat of concentrated Callisto (see Chart Book or contact me for more details).
A single application may knock it back a little, but two are needed to see significant control. After the PI recovers from the first treatment (now-ish) and spends more resources on making new leaves, hit it again (4 weeks or so later). Remember you can only make 2 applications of Callisto per bed per year.
The Special Local Needs (24c; SLN) that permits the use of a concentrated solution is only available for Callisto; the other generic mesotrione products do NOT have this special labeling and cannot be used in this fashion.
Most growers are hesitant to spray herbicides during bloom for fear of damaging the flowers or stressing the vine. In general, if you don’t have to spray herbicides during bloom, it is best to avoid doing so. However, herbicide efficacy is often based on growth stage of the weed, so if you need to spray during bloom, you can usually do so without impacting the crop. We have not experienced or heard of growers having issues with using Intensity One or Callisto during bloom, and NIS appears to be safe for use with these herbicides during this timing too. Crop oil carries a risk of injury to plants and delicate flowers. Avoid using crop oil during bloom and any other time that it is hot and humid:
[air temp (ºF) + relative humidity = +150].
Disease
The final Keeping Quality Forecast is POOR. See the keeping quality forecast for more detailed info. Many growers applied their first fruit rot fungicide this week. Most fruit rot infections occur during the bloom period and early fruit set, before berries start to size up. Your first application should happen when 10-50% of flowers are opened. Once the fruit has set and begun to increase in size (mid-late July), fungicides are no longer necessary or effective for fruit rot management.
Here are some answers to frequently asked questions about fruit rot fungicides!
Which are contact fungicides, and which are systemic?
Contact fungicides do not enter plant tissue and act only on the surface to protect against infection. Systemic fungicides penetrate plant tissue and may move within the plant (locally or fully systemically).
These are contact fungicides, which are multi-site, protective, and not systemic.
- Chlorothalonil products (Bravo, Echo) – FRAC M5
- Mancozeb products (Manzate, Dithane, Roper) – FRAC M3
- Copper-based fungicides (Badge X2, Kocide 3000, Champ WG, etc.) – FRAC M1
These are the systemic fungicides, and they are single-site fungicides with translaminar or limited systemic movement, offering both protective and some curative activity during early infection periods (if applied immediately after infection).
Prothioconazole (Proline, Prozio) – FRAC 3
Fenbuconazole (Indar) – FRAC 3
Azoxystrobin (Abound, Quadris, etc.) – FRAC 11
Difenoconazole (in Quadris Top) – FRAC 3
If you apply a fruit rot fungicide when there are closed pods, do they get any benefit or are only open flowers benefiting from fungicides?
Only open flowers and tissue present at the time of application receive protection from contact fungicides.
- Contact fungicides (e.g., chlorothalonil, mancozeb, copper) won't protect tissue that develops after spraying.
- Systemic fungicides may offer some protection to developing tissues due to their movement, but effectiveness still depends on timing and mode of action.
Thus, closed pods at spray time may receive limited to no protection, especially from contact fungicides.
What is the difference between “broad spectrum” and “single-site”?
- Broad-spectrum fungicides (e.g., chlorothalonil, mancozeb, copper) act on multiple sites in fungal cells, affecting several biochemical processes. This makes them less prone to resistance.
- Single-site fungicides (e.g., Indar, Abound, Proline) target a specific site or enzyme in fungal metabolism. These are more prone to resistance and often used in rotation or mixtures.
In short:
- Broad spectrum = multi-site, low resistance risk
- Single-site = targeted, higher resistance risk
What are protective vs curative fungicides?
- Protective fungicides are applied before infection occurs to prevent fungal establishment. Protective = preventive
– e.g., chlorothalonil, mancozeb, copper - Curative fungicides are applied after infection, targeting the fungus during early stages of infection (latent period).
– e.g., systemic fungicides like Proline, Indar, Abound have some curative potential if applied soon after infection, but are also preventive.