We have had some extreme weather in Wisconsin this spring. Throughout the Northeast and Midwest, an unusually long warm spell propelled us into spring in early-mid March. While many of us were hoping that the warm weather would last, we were not so fortunate. Multiple nights of hard frost and daytime temps barely and rarely hitting 60 characterized the month of April. People have been asking us, “What are the effects of this crazy weather for insects and for crops?” I have been out doing field work throughout the past month, visiting apple orchards in southern Wisconsin where I study wild bees, and I have observed the potential effects of the weather on pollinators and pollination. Two phenomena related to the weather have occurred this spring, both potentially reducing this season’s fruit crop. In a typical year, fruit trees don’t bloom till late April or early May, after the risk of frost has largely passed. This year, however, with warm temperatures, fruit trees bloomed in early April. Frost then hit many orchards when some trees were in full bloom. While flower buds can better withstand freezing temperatures before they are fully open, hard frost during bloom will destroy the flower and prevent fruit formation. For the late bloomers that escaped the frost, their reproductive success may not be much improved. Cool weather during bloom means fewer bees active and flying, as bees don’t like high winds or low temperatures. Without bees to pollinate, fruit will not set on these trees either. Compared to 2010 and 2011, I have seen dramatically fewer bees visiting blossoms and in my trap samples. However, all a farmer really needs is one, warm day during bloom to ensure a decent crop. And, some of the hardier bees, like bumble bees, will fly in 50 degree temps. So, while it is still too early to give up hope on an abundant tree fruit crop, I predict that yields will be lower this year due to frost and poor pollination weather.
Posted by Rachel Mallinger