Pre-harvest pest problems in vineyards, 2022

Managing Botrytis bunch rot

Berries become susceptible to direct infection by Botrytis once fruit reach veraison.  Under conditions of high humidity, a single berry infection can quickly spread to involve the entire cluster.

To reduce the risk of fungicide resistance, if sporulating infections are present, I recommend drying up the infections first with a fruiting zone spray of MilStop (potassium bicarbonate) followed by one of the products with Botrytis activity (see table below).  MilStop will increase the pH, which may reduce the effectiveness of a Botrytis fungicide so check with the company to confirm whether a tank mix is recommended.  I’ve heard reports that Folpan and sulphur may also dry up Botrytis infections and these can be tank mixed with a Botrytis product unless specified otherwise on the label.  Make sure that you consider fungicide group rotations and avoid using products from the same group in back-to-back sprays.

Fungicide	Group	Botrytis	PHI
Elevate	17	4	7 days
Kenja	7	4	14 days
Scala	9	4	7 days
Intuity	11	4	10 days
Switch	12	4	7 days
Inspire Super	3+7	4	14 days
Luna Tranquility	7+9	4	7 days*
Miravis Prime	7+12	4	14 days
Diplomat	19	2	0 days
ProBlad Biofungicide	BM1	3	0 days
Serifel	BM2	3	0 days
Botector	NC	2	0 days
Double Nickel	NC	2	0 days
Timorex Gold	NC	3	When dry

* Bayer CropScience recommends 45-day PHI

Waxy grape berries are difficult to wet. Some research suggests that the use of wetters (a type of adjuvant) may improve late-season control of botrytis. Read the product label or ask the chemical supplier as most product formulations already contain adjuvants and too much wetter added to the tank mix can result in less chemical being deposited on bunches.

Managing Sour rot

Sour rot is caused by acetic acid bacteria and yeasts that reside on the outside of the fruit.  Infection frequently starts in the centre of the cluster where berries are squeezed as they swell.  Drosophila spp (“fruit flies”) are excellent vectors of these organisms and can rapidly spread the disease throughout a vineyard.

Research in Ontario and New York has shown that applications of antimicrobials such as potassium metabisulphate (KMS at 5 kg/1,000 L) or peroxide (Oxidate) in combination with insecticides were the most effective way to manage the disease.  Optimize drying conditions through canopy management and crop thinning to avoid clumped clusters.

Manage insects as well

It is critical to manage not just the yeasts and acetic acid bacteria that cause sour rot, but also the Drosophila flies (spotted wing Drosophila as well as the common “fruit fly) that can carry and spread them.

Wasps or yellow jackets are attracted to the juice that leaks from damaged berries. They also have mouthparts that are capable of puncturing berry skins to get to the sweet insides.

Earwigs seemed to be present in almost every cluster I examined last week.  While they don’t damage clusters, some research in Europe found that wine made from Pinot noir contaminated with 10 earwigs/kg of fruit was described as reductive, acidic and vegetal. I don’t know that we’re at that level of infestation yet.

The most effective labeled treatments for SWD (and common fruit flies) are Delegate and Success and they both have activity vs wasps and earwigs, but not MALB.

Insecticides	SWD	Wasps	MALB	Earwigs	PHI
Malathion	1	1	4	3	3-4 days*
UP-Cyde, Ship, Mako, Ripcord	3	4	4	3	2-7 days*
Delegate	4	3	0	3	7 days
Entrust	3	3	0	3	7 days
Success	4	3	0	3	7 days
Harvanta	4	0	0	0	7 days

*PHI for machine vs hand harvest

Is it worth it to keep spraying?

There will be seasons when we must accept that very favourable weather for botrytis can undo our best efforts in the vineyard. A season-long spray program may not be enough to control botrytis when the risk of disease is very high.

In wet seasons, it can be very tempting to keep on spraying as long and as much as possible; however, once botrytis becomes highly visible in the vineyard and the weather forecast is for ongoing rain, it sometimes can be more cost-effective to do nothing and harvest as much as possible and as early as possible, if you have this ability. Under these conditions, spraying provides very little, if any, extra benefit relative to the cost (e.g. fuel, labour, fungicides). Maintain close communication with your processor regarding harvest timing and requirement for pesticide applications.