T he first thing Broc Zoller does every morning is check the weather forecast. For the past five years, California farmers like him have struggled through historic drought. Now they face the opposite problem. In the first months of 2017, it has already rained more than it did all of last year in Kelseyville, where Zoller grows wine grapes and walnuts, and leases out land to pear growers. The muddy conditions have slowed pruning efforts and delayed the application of sprays used to control key insect species over the winter. If the rains continue as spring arrives, the combination of warmth and wetness could spark fungal and bacterial infections. To protect his crops, Zoller suspects he will have to use several conventional pesticides.But the selection is getting slimmer, thanks to resistance. Fire blight, a bacterial disease that can cause weeping cankers on pear-tree trunks, generally responds to antibiotics, but the drugs can stop working if overused. And pear scab -a fungus that leaves unsightly brown lesions on the fruit -calls for multiple fungicides throughout the growing season. Zoller, who also works as an agricultural pest-control adviser, uses some of these chemicals just once before they start to lose effectiveness. "The resistance comes so quickly, " he says. "You hope there aren't too many rains so that what you have in your arsenal can get you through. "Resistance to conventional pesticides -among insects, weeds or microbial pathogens -is common on farms worldwide. CropLife International, an industry association based in Brussels, supports efforts that have counted 586 arthropod species, 235 fungi and 252 weeds with resistance to at least one synthetic pesticide (see 'The rise © 2 0 1 7 M a c m i l l a n P u b l i s h e r s L i m i t e d , p a r t o f S p r i n g e r N a t u r e . A l l r i g h t s r e s e r v e d .