Tips of Hybrid Willow cuttings are Dying

tobler

I have 72 hybrid willows that I started in March from cuttings from our own trees which were still dormant (I'm in southern Michigan). I have them in 4"x14" tree pots in nearly full sun in a small "Culti-Cave" greenhouse which I used to protect them from cold nights, direct precipitation and high winds. Once the weather warmed up, I removed both ends of the greenhouse, and today, I removed the entire greenhouse.

The cuttings have all seemed healthy and are now a wispy 3' tall with generous, happy green foliage. Twice, I've spayed them lightly with a plant-safe insecticide intended for vegetable plants.

My problem is this: beginning a few days ago, when the weather hits 80+ degrees and the day is mostly sunny, the tips of several trees completely wilt very suddenly by early afternoon. It entails the top 3-4" of newest growth which goes from looking great in the morning to dangling completely limply by 2pm and then dying by the next day. The rest of the plant seems fine. There is no discoloration; the leaves wilt while bright green.

I've kept these guys well watered, but not soaked, and check on them several times a day as they've always been right outside my door against the south side of the house. The tree pots are black plastic, but don't feel hot to the touch.

Any ideas on what I'm dealing with and what I should do now?? Thanks!

Worried Wendy

Brent Ferris

I believe the trees were exposed to too much heat too fast. The tops were transpiring water faster than they could take it in, and the tops died. Until they can be outplanted, less sun especially in the heat until they acclimatize. And unless there is a visible bug problem, skip the spray-fertilizer.

tobler

I was hoping it was something this simple, despite the fact that they've been in this same location since day one, so should've acclimated to the sun and heat. This wasn't our first bout of heat, but they've grown so fast, your description of transpiring faster than intake probably explains it as they were never this large on the previous hot days.

I did the bug spray (no fertilizer involved) because there were indeed bug problems.

Thanks so much for your input! This gives me continued hope that there's not a disease involved. Actually, since I posted, only a couple more tops died and all has been fine since then. About 14 trees out of 72 were affected.

tobler

I should add that the reason I'd felt they'd acclimated fairly normally was because the clear plastic Culti-Cave greenhouse is only 3' from front to back, so when I unzipped and removed its large "doors" a few weeks ago, my cuttings were in direct sun.

Brent Ferris

I can see why you would think they would be acclimatized to the sun, but if the cover was still over them, would the humidity for the tops be higher, than if exposed to the air and sun?

tobler

True, the humidity was probably a bit higher even with just a 3' wide cover. Also, the wind, even though it seemed to be able to "whip" through there, was undoubtedly lessened. So, I guess I suddenly stressed them more than I thought! Good! It beats a disease! LOL