HGIC received its first allium leafminer (Napomyza gymnostoma) question from a Baltimore gardener. The pest symptoms were discovered on chives growing in a window box. If you observe this pest please send photos and information through Ask an Expert.
Mated female flies lay eggs on lower leaves and the hatched larvae feed on leaves, creating visible trails (mines) between leaf surfaces. They pupate in protected plant parts (bulbs. leaf sheaths) and a second generation of adults emerges in September and lays eggs. Larvae feed and overwinter in the pupal stage inside infested plants and adjacent soil.
A floating row cover can be used to exclude adults in spring and fall when they are flying and searching for host plants. Neem oil and spinosad are organic insecticides that may be effective in controlling allium leafminer. Here is some detailed information from Penn State (this European pest got its U.S. start in PA in 2015) and UME about the allium leafminer.
Last year’s blog post has 5 tips for people who are ready to plant!
Spring Weather Is Tough on Seedlings and Transplants
And for those who could not wait…erratic spring weather is hard on the tender transplants of warm-season vegetable crops. Leaves that are yellowed, bleached, bruised, torn, punctured, spotted, and discolored are showing symptoms associated with challenging spring growing conditions. These include high winds, cool night temps, cloudy and rainy weather, and rapidly fluctuating air temperatures, etc. In addition, soil temps are relatively low, so root systems are slow to grow, pick up nutrients, and become established. Under such harsh conditions plants just sit and get beat up by the elements.
Pepper grows more slowly than tomato so expect plants to struggle for a while as they get established. The recent cool nights will not have much effect on later flowering and fruit set, but do pinch off pepper blossoms for 3-4 weeks to get strong root systems.
For tomato, night temperatures below 50-55 degrees F. typically cause pollination and fruit development problems (even though only buds are exposed) resulting in “catfacing” of tomato fruits (crevices, hollows and holes).
There is no way to prevent this other than holding off on transplanting until late May. Cultivars vary in the degree to which low night temps will negatively affect fruit. It’s typically best to immediately remove these fruits as they don’t develop or ripen well – only a small portion of each affected fruit may be edible.
New Basil Cultivars with Resistance to Downy Mildew
Four new basil cultivars with downy mildew resistance are available for home gardeners- ‘Obsession’, ‘Devotion’, ‘Prospera’, and ‘Amazel’ (sold as plants). Seeds can be ordered from some online vegetable seed suppliers. ‘Amazel’ plants may be difficult to find at this time.
‘Prospera’ and ‘Amazel’ may be the best bets at this point, based on 2018 results from a Cornell University research trial.
Fabric Grow Bags
Many more types and sizes are coming on the market and gardeners seem to really like them. They are versatile, reusable, and affordable. Plant roots are air-pruned when they reach the breathable fabric. This promotes root branching and a larger overall root system. Here’s a 5-gallon bag (with handles) that we planted with herbs for Maryland Day on April 27th:
What’s in the Bag?
Be selective when buying growing media to fill containers. Products can vary greatly and carry an assortment of names- potting soil, topsoil, planting mix, etc. Look for products that are soilless (no sand, silt, or clay), are homogeneous in appearance, fairly lightweight when dry, and smell earthy. A 1:1 mixture of compost and a soilless growing medium works well for most container gardens. Our “Soil for Containers” web page has more information.
By Jon Traunfeld, Extension Specialist