Foliar Fungicides Help Maize Farmers Reduce Yield Gaps in Late Sown Crops in a Temperate Region

Foliar diseases produce significant maize (Zea maize L.) yield reductions, increasing yield gaps and threatening food security. In the central temperate region of Argentina 50 % of maize cropped is grown under late sowing dates (December), where meteorological conditions are favorable to disease development, such as higher temperatures during initial stages and higher relative humidity. However, no major testing was reported to fully understand yield responses to foliar fungicides. Our objectives were to quantify the impact of foliar fungicide application on grain yield in late sown crops, and to identify genotype, management, and environmental interactions modulating the yield response. We conducted 21 on-farm trials during 6 growing seasons (2014/15 and from 2016/17 to 2020/21) with and without a fungicide, each trial having 8-20 commercial hybrids. Fungicide application was done between V8 and V12 stages (eight and twelve fully expanded leaves, respectively), using a commercial fungicide mix of azoxystrobin and cyproconazole. Average yield variation across sites ranged from 4359 to 12,101 kg ha- 1, and fungicide use produced an average positive yield increase of 472 kg ha- 1 (or 5.8 %). The yield increase varied from no response to 1282 kg ha- 1 across sites, and was not correlated to the site yield. Fungicide application explained 1.9 % of the total yield variation, higher than its interaction with either site or genotype (1.1 and 0.1 % of total yield variance, respectively). Mean temperature from sowing to V14 (fourteen fully expanded leaves) helped explain the crop yield response variation to fungicide application across sites, increasing by 138 kg ha- 1 degrees C- 1 in response to higher mean temperature (explored temperatures from 21.9 to 26.4 degrees C). Our results illustrate the relevance of fungicide applications to reduce yield gaps, where described predictors can help farmer optimize this decision.