The effect of roadside mowing and fertilizer use on milkweed (Asclepias syriaca) populations in central New Jersey

Background/Question/Methods

Common milkweed (Asclepius syriaca) levels have been dropping over the past several decades. As caterpillars, Monarch butterflies (Danaus plexippus) eat milkweed as a sole food source and are a big source for pollination in the US. Roadside mowing and fertilizer use in maintained areas may partially be responsible for this decline in milkweed. The hypothesis was if roadside mowing and fertilizer use takes place then milkweed populations would be less than in areas not maintained. In this field based survey, all of the milkweed patches in publicly accessible areas of Montgomery Township NJ were measured. The following measurements were collected: altitude, number of stalks, GPS coordinates, recent fertilizer or mowing status. GPS data was collected using GPS Tracker 1.0 for Blackberry. Data was organized into a spreadsheet and graphed using OpenOffice.org 3.3.0.

Results/Conclusions

A total of 482 stalks were found in 30 patches. None (0/30) of the patches were from areas recently mowed, and 10% (3/30) were found in areas recently treated with fertilizer. The average altitude of patches was -3.67 meters. The average number of stalks in each patch was 16.1 (range 1-180). There was no relationship between altitude and the number of stalks in each patch. In this study, we conclude that in biomes similar to central New Jersey, common milkweed rarely grows in areas recently treated with fertilizers or that have been recently mowed. More needs to be done to cultivate and encourage growth of this important plant.