We're currently seeing heat stress in our raspberries. It started showing up even before it got extremely hot, but it was limited to one here and there. But the past couple of days we've seen it really hitting the Heritage variety of raspberries. What we're seeing are some white drupes within the drupelet.
- Drupe - The fleshy fruit with a single seed. In a raspberry or blackberry, it would be each of the individual tiny round balls of fruit that make up a cluster in what is considered the berry.
- Drupelet - The individual drupes that in composite are considered the berry on plants such as raspberry or blackberry.
So what we're seeing is called White Drupelet Disorder. Looking that up I found that it can be caused by a handful of issues, but one being excessive heat.
Imagine that? A plant that's in a greenhouse, even with its sides open and the end-wall door wide open, would show signs of heat stress in NW Iowa from this past week. The high tunnel weather station showed a hight temp of 109F two days ago. I'd say that qualifies as excessive heat. The Heritage raspberry variety is more susceptible to the disorder, and the variety showing the most symptoms is Heritage, but the others that are producing right now are showing it here and there too. They don't taste any different, but they aren't very pretty.
