Powdery Mildew in the Vineyards of Qazvin, Fars, Azerbaijan and Khorasan

Powdery mildew of the vine takes part of the crop every year in the vineyards of Qazvin, Takestan and Abyek, of Marvdasht and Bavanat in Fars, of East and West Azerbaijan, and of Kashmar and Razavi Khorasan. This disease does not belong only to the humid air of the north. The agent lives on green surfaces and advances in hot, relatively dry weather too, especially when the leaves are sitting on top of one another and the airflow has stopped. Damage on young berries shows as russeting, cracking and corkiness, and on the leaves as a white to greyish powder. Growers who wait until the mildew is plainly visible have usually already lost one round of reproduction. Successful control starts from phenology and canopy ventilation, not from changing the name of the fungicide every week.

Before flowering and after fruit set: two windows that must not be left empty

The mildew cycle starts from buds infected the previous year and from tiny colonies on the first leaves. Young tissue — a fresh leaf, the inflorescence, a small green berry — is the most susceptible surface. A preventive round before flowering keeps the primary colonies down. A round after fruit set covers the bunch during the period when cracking and russeting ruin its marketability. In Qazvin those two windows often coincide with rapid shoot growth in May and June. In Fars both may come earlier. In Azerbaijan and Khorasan, altitude and spring cold shift the calendar; copying a Qazvin neighbour's dates in a cold-climate vineyard is wrong. The interval between the two rounds is set by the speed of shoot growth, washing rain and dust, not by a fixed number on a wall calendar.

Calendar spraying with no regard to shoot growth, or continuing to spray after bunch closure without a reason, or too long a gap between rounds when the shoot is putting on several nodes a week — that is what builds a control failure. The aim is not to add a new product to the vineyard every week. The aim is that a protective cover stays on the susceptible tissue. If rain or dusty wind has washed the cover off, run the same programme again with a fresh cover; you do not necessarily have to change the chemical family. Writing down the dates of bud break, the start of flowering, fruit set and bunch closure on the plot's sheet is more useful than memorising fungicide brand names.

Do not spray sulphur in the midday heat

Sulphur is still the pillar of prevention in many Iranian vineyards. At very high temperatures it burns leaves and berries, and at very low temperatures its effect falls away. Hot June middays in Qazvin and Fars are the wrong time to apply sulphur. Move the work to the cool of the morning or to the evening after the temperature drops. Do not wet a thirsty vine with sulphur either; water stress intensifies the scorch. Do not combine sulphur with oil products or certain mixes without knowing what you are doing. Alternating with other fungicide groups makes sense when disease pressure is high or when the sulphur round cannot deliver the cover. Repeating one chemical family all season shortens the road to resistance. This article is not the place for a commercial list. What must stay on the vineyard's sheet is the phenological date, that day's temperature and the quality of the cover inside the canopy.

Air inside the canopy is the cheapest fungicide

Powdery mildew is more severe in a closed canopy, on shoots collapsed over the wire, and on plots whose rows run across the prevailing wind. Green pruning, removing suckers, and opening the area around the bunch at the right time reduce surface moisture on the leaf and improve the penetration of the spray. In traditional vineyards of Khorasan and Azerbaijan trained low or semi-prostrate, contact between the bunch and the soil and permanent shade keep the disease going. Lifting the shoots onto the wire and thinning the centre of the vine sometimes does the work of two spray rounds. Overhead sprinkler irrigation onto the canopy at midday is not ideal for mildew; if you have no choice, confine the timing to early morning so the leaf surface dries. Stripping leaves indiscriminately in the heat of Fars scorches the berries themselves; opening the area around the bunch is different from tearing leaves off wholesale.

• Before flowering: thin the canopy so the first leaves get light and air.
• After fruit set: open the area around the bunch; in the heat of Fars do not strip the leaves all at once.
• Take heavily infected shoots and leaves out of the vineyard; do not leave them between the rows.
• Design new row plantings with the prevailing wind and enough space between rows.

A susceptible cultivar and excess nitrogen mean more pressure, not a separate programme

Some local cultivars and some commercial ones are more susceptible to powdery mildew. Account for the cultivar's susceptibility in the interval between rounds, rather than writing one calendar for every vineyard. A vine that has had too much nitrogen and built dense soft growth is a better host for mildew. Avoiding late nitrogen is part of disease management. A weak vineyard and an over-fed vineyard can both get severe mildew: one because moisture lingers and growth is slow, the other because the tissue is soft. Cultivar resistance is not complete immunity. Even a low-susceptibility cultivar takes damage in a closed canopy with no cover before flowering. Do not separate training and nutrition from the pesticide file.

1. Record the phenology: bud break, pre-flowering, fruit set, bunch closure.
2. Put the first round on preventively and before you see any white powder, especially on a plot with a history.
3. Set the sulphur against that day's temperature, and check the cover inside the canopy after spraying.
4. Treat green pruning and training as part of the disease programme, not as the pruner's separate job.
5. If a round fails, look first at the interval and the coverage, and only then change the product.

Powdery mildew in an Iranian vineyard becomes chronic through wrong timing, a closed canopy and spraying in the heat. Sulphur and other treatments work when the cover reaches the leaf and the susceptible tissue is not left unprotected. Qazvin, Fars, Azerbaijan and Khorasan each have a slightly different calendar, but the principle is the same: the two windows before flowering and after fruit set, air inside the canopy, and the temperature on the day sulphur is applied. In vineyard consultancy, Farin Kesht Taban ties the disease programme to training and nutrition, not to a long list of fungicides.