What the Heck ...?
Tree Fruit IPM Update 1 May 2019
The past six months or so I've severely reduced the amount of time I am on social media, especially FaceBook, so I miss a lot of cat videos and other "cool stuff." Yet, there I was today when I came across this scary weather forecast about a massive arctic airblast descending on Europe. It is so massive that the temperatures could fall into the upper-teens across eastern France, and into parts of Spain and Africa. It will be worse in Scandinavia, but still almost all of Europe will feel the impacts. While this is a long way from the second coming of the Ice Age, you have to ask yourself - or, I did anyway - why is this happening? What the Heck is Going On?!
To be sure, I am not a climatologist. I don't claim to be, don't want to be, but because weather impacts not only what I do, but what my friends, colleagues, and clients, do as well, I need to stay abreast of what's happening with the weather and why. So here it is, simply and in my own words.
What's happening in Europe is akin to the polar vortices we experienced in North America this past winter. Typically, these cold air masses are always around and centered at the north pole. They usually stay there because they are strong and generally "penned" in place by a strong jet stream . However, when they weaken - and it happens all the time - they tend to wander and drift south. A strong jet stream moderates their drift and keeps them further north. But as the jet stream weakens due to the melting ice caps, there isn't anything to keep the cold air from drifting into Europe, Spain and Africa. So while these polar vortices have existed forever, in both strong and weak states, the forces (i.e., jet stream) keeping them in place have weakened significantly. And there seems to be a more consistent weakening of the polar air masses over time, though no one is quite sure why. It would be great to blame their weakened state on Exxon, but we can't. However, we can blame global warming and the melting ice caps on industrial globalization.
The real issue at hand is how do we address these until recently unlikely late season freezes and continue to farm successfully? It is likely that farmers across Europe will incur losses from the impending cold air and frosts. We in North America may be successful in dodging a bullet this winter/spring (though it was 23F at my house the other morning), we also may not - we'll just have to wait and see. While we can't do anything immediate to address global climate change in the immediate term, we can grow healthier crops, crops that are more resistant to cold damage and frosts. And in order to do this we must build up the strength of the soils by sequestering more carbon that in turn holds more nutrients and biological activity, that in turn removes CO2 from the atmosphere and reduces the impact of climate change. That in turn gives the plants what they need for healthy tissue and innate resiliency. So I guess we can have our cake and eat it, too!
Well, sort of. These weather anomalies cause other problems in the natural world that throw the balance of nature into question. We have to be aware that while our trees can and will suffer from time to time, the affects on pollinators, beneficial insects, birds, bats, flowering plants, and the like is equally disturbing and affects the vitality of our orchards and farms. In the short term, it might be a rough year for French wines, but in the long term the whole of nature is being thrown into a conundrum. While we might be able to have our cake and eat it, too, we have to still grow the grain for flour and cocoa for chocolate to make the cake. Bon appetit!!
Yessiree, it's now officially May, though you might not know it by looking at your thermometer the past few days. Ok, it’s not been that bad, but it was 23F at my house Monday morning and there were regular reports of low 30s and upper 20s all over the place. The cooler, wetter, cloudier conditions have slowed things down a bit, but the band keeps on playing.
APPLE SCAB - The threat for apple scab is literally off the charts. Both NEWA and RIMpro show very high infection potential for the next 4 days (including today, as I write this). But it is May 2/3 that contain the highest threats. Western New York is at a higher RIMpro threat potential than eastern NY, but everyone should be fairly warned that if you're orchards have not been sprayed for scab, that you will need to react quickly after the rains to catch up. The good thing is that by the weekend, eastern NY will be roughly 75% through primary scab season, while western NY will only be 30% through primary scab season. While this is good news, there is still a long way to go and with cooler weather, ascospore maturation should progress more slowly extending primary season more than if it was very warm.
FIREBLIGHT - Eastern NY does have some southern orchards with open blossoms. Still a long ways from full bloom, but progressing there quickly enough. RIMpro does show a critical fireblight infection period beginning about May 4 - though NEWA is less enthusiastic. The cool temperatures have reduced the threat because of a lack of heating units needed to grow the requisite epiphytic populations of Erwinia spp. So while everyone should be safe through this next week, be prepared if the temperatures rise and more blossoms open, increasing the threat. If you are an organic grower and have had a history of fireblight your options for control are limited. Unlike conventional growers, you can’t apply traditional antibiotics. You need to begin to prepare now for the likely fireblight infections headed your way.
BROWN ROT - Plums and apricots are at petal fall, so while the BR threat is reduced it is not gone. Peaches, cherries, and prunes are all in bloom (various stages) and wide open to BR infection, so be prepared!! This is also the time that grey mold infections can begin, though symptoms won't appear until harvest.
INSECTS – I am still not seeing much in the way of insect activity, though a few rogue gypsy moths and some small woolly apple aphid colonies, but nothing of critical importance. As apples, and especially stone fruit, move through bloom and towards petal fall, there are several insects that do create some concerns. In apples, European apple sawfly is the primary apple pest during bloom. It is too late to apply anything, but if a pink insecticide was applied, then your flowers should be protected. Soon, plum curculio will be active and causing damage. In stone fruit, this can begin between shuck split and shuck fall, in apples and pears it can occur at petal fall and continue on for 309 DD43. I am not quite at a point where this is a concern, but be prepared. Finally, black stem borer is active and causing damage. Though this is earlier than where we might normally do much, with all the damage we've seen over the years it is never too early to at least start trapping. In fact, we've already seen this year where young orchards are being attacked and trees suffering some damage. Not much, but any damage is a concern.
THINNING – We’re still a ways away from fruitlet thinning in apples or pears, but it is never too early to start thinking about blossom thinning, especially in eastern NY where trees are just starting to come into bloom. Western NY has at least a week before blossoms open. Cornell has posted their Pollen Tube Growth Model on NEWA so you can better time any bloom thinners. What's that you say? well, don't underestimate the power of a well-timed bloom or petal fall thinning spray. when done well, they really take the heat off of the fruitlet thinners. And when it is so cool and cloudy and rainy, there is less Pn going on and trees are more stressed, so anything you can do to lighten the load is welcomed (by the trees, not me so much). Stone fruit thinning (blossoms) should have already occurred with either thinning or pruning, or both. If not, it's not too late in some instances, but for apricots and plums you'll have to now wait for a while and thin fruitlets.
