On May 20, I ran the MaluSim carbohydrate model for Winchester and Central Virginia. This will be the last MaluSim posting using forecasted data for the season. Sometime in the week or two I will post a season recap using only recorded data.

In Winchester, as predicted, we have been experiencing hot and cloudy weather over the last few days. Thinning applications made from late last week through Monday will likely be fairly active, with some easy to thin cultivars (e.g. Red Delicious) potentially having significant fruit drop. However, from Tuesday through the end of the coming week, growers should expect an average response from their thinning applications.

In Central Virginia, there was a similar trend but with somewhat cooler daytime temperatures, the carbohydrate deficits were less severe. Similar to Winchester, thinning applications made over the next several days should have a fairly typical response.

Peck Winchester VA MaluSim 5_20_13

Peck Central VA MaluSim 5_20_13

Fruitlet sizes and growth rates at the Winchester AREC:

• Empire: 19.1 mm; 1.5 mm/day
• Fuji: 13.6 mm; 1 mm/day
• Gala: 13.8 mm; 0.8 mm/day
• Pink Lady: 14.1 mm; 0.9 mm/day
• Red Delicious: 13.8; 0.9 mm/day

MaluSim carbohydrate models for Winchester and Central Virginia were run on Thursday morning.

Over the next day or so, for Central Virginia, the carbohydrate balance will remain in the negative, but quickly move to the positive over the weekend. From thinning applications made Thursday (5/9) or Friday (5/10), growers should expect a fairly “normal” response. However, forecast data from Intellicast.com, suggests that sunnier, but cooler weather will move into Virginia early next week, followed by a warming trend starting on Wednesday. Based on the MaluSim model, this weather pattern will cause apple trees to have positive carbohydrate values through the early part of next week, and thus standard rates of thinners used on Saturday or Sunday will be less effective than expected. In blocks where heavier thinning is needed, growers should consider holding off on their 10 mm thinning application until Tuesday or Wednesday when warmer temperatures return. However, once fruit gets to be 15 mm or larger, NAA and 6-BA are less effective thinning agents. The other approach is to increase the rates used in thinning applications made over the weekend through Monday.

The above scenario is similar for Winchester but since fruit size is smaller (generally 6-8 mm), growers can wait for next week’s warming trend to make the 10 mm thinning applications. Additionally, with the smaller fruit size in Winchester, the cloudy weather that we’ve experienced over the last few days should cause less natural thinning than what might occur in Central Virginia.

I’ll run the model again on Monday.

Current fruitlet sizes at the Winchester AREC:

• Empire: 8.0 mm
• Golden Supreme: 6.3 mm
• Fuji: 6.5 mm
• Golden Delicious: 5.7 mm
• Suncrisp: 6.0 mm
• Pink Lady: 7.2 mm
• Idared: 7.1 mm
• York: 6.0 mm

For more information, download pdfs of the models:

Peck Central VA MaluSim 5_9_13

Peck Winchester VA MaluSim 5_9_13