Protect Seedlings - Beet Leafminers

Coastal gardeners who did a lot of planting in the first really warm weather last weekend had a taste of what it is like to garden in the rest of Canada, where gardens are traditionally planted all at once on the May long weekend. By now, even the most delicate plants can be set outdoors—I hope!

I thought I should send a reminder to shade your seedlings and newly seeded beds over the next few days and in any subsequent heat waves. The forecast is for high temperatures of up to 28-30oC (82-86oF) inland, away from cool breezes off the water. Temperatures that fry seedlings right now wouldn’t burn mature plants later in the summer when roots are deeper, leaves shade the soil and leaf cells have adapted to heat. If you are starting carrots, lettuce or parsnip seeds right now, the soil could be too warm for good germination so cover these and other seedbeds to keep the soil surface cool until the first tiny green leaf appears. Use burlap, old towels, newspaper, opaque white plastic, etc. If it is still hot when the shoots appear, trade the soil cover for a tent of shade cloth, lattice work, leafy branches laid over the soil or anything that partially shades the bed while letting in about half the sun. Lacy curtain material or cheesecloth can be used for a couple of days, but they don’t let in enough sunlight for long use; better to deploy those materials in the hottest part of the day and uncover plants for morning and late afternoon sun. Materials not to use are floating row cover or insect netting—these both trap heat. If you are using these to keep carrot rust flies or other insects from lay eggs on plants, lay the shade material over the top of the insect cover.

I noticed yesterday that leaves on my strawberries, which are much bigger than usual due to the cool spring weather, were showing signs of sunscald. Those few hot afternoons on the weekend were enough to injure areas of such soft leaves most directly exposed to the sun. A couple of days after high temperatures occur, sunscald shows as pinkish or browning patches between leaf veins and around leaf edges. Later, the patches become dry and brown or yellow. Sunscald injury happens to all affected leaves at the same time and looks directional, meaning that it affects leaves on the sunniest side or on top of the plant. You can distinguish it from diseases because infections tend to progress over time, usually starting with oldest leaves. Leaf diseases often infect shaded and interior leaves first, where the leaves stay damp the longest after rain or irrigation. If it really gets hot this weekend, I plan to throw shade cloth over my cabbage family plants, just to keep them happy (particularly those persnickety cauliflowers that really don’t like heat).

Pest du jour: Eggs of the first generation of beet/spinach leafminer have been laid on spinach, chard, rhubarb, beet, French sorrel (see damage and egg masses). These tiny, chalk white, masses are actually fairly easy to see on the undersides of leaves. When the eggs hatch, the leafminer larvae move between the upper and lower surface of the leaf, feeding on the cells in between. The larvae are safe from sprays and most predators once they are inside the leaf. You can control them right now by harvesting the leafy greens (but don’t cut beet leaves). You can easily wash off the eggs (or pick out small damaged areas, if the miners have started mining) and store the leaves in the refrigerator. Plants grow another crop of leaves, but the first generation of leafminer won’t get a chance to mature and that’s often all you need to do to keep damage low. There are 2-3 generations per summer, but if you get a good jump on the early eggs, later generations are smaller and later eggs are also more likely to be eaten by lady beetles and other predators. If your plants are being hit by high numbers of leafminers, then grow the next crop under insect netting or floating row cover to prevent leafminer adults from laying eggs. Damage to beet leaves usually doesn’t have much impact on the roots (you can pick off damaged parts of leaves, but don’t remove whole leaves as that will slow root development).

Happy seedlings in the cool shade.

About Linda A. Gilkeson, Ph.D.

Salt-Spring---Linda-GilkesonLinda earned a Ph.D. in Entomology from McGill University in 1986, then moved to British Columbia to work for Applied Bio-Nomics Ltd., a company that produces biological controls. From 1991 to 2002 she worked for the provincial government, promoting programs to reduce and eliminate pesticide use. She was head of the provincial State of Environment Reporting Unit for the next six years, then the Executive Director of the Salt Spring Island Conservancy until the end of 2011. Linda now devotes her time to writing, teaching and consulting.

Linda has co-authored pest management training manuals for the government and organic gardening books for Rodale Press. She has self-published two books: Year Around Harvest: Winter Gardening on the Coast and West Coast Gardening: Natural Insect, Weed and Disease Control. Her recent book, Backyard Bounty: The Complete Guide to year-Round Organic Gardening in the Pacific Northwest, has become a BC best seller.

As a private consultant, Linda is a regular instructor in the Master Gardener programs in BC and is busy year around giving workshops on pest management and organic gardening.

Linda has served as President of the Entomological Society of Canada, the Professional Pest Management Association of BC, the Entomological Society of BC and the Salt Spring Island Garden Club. She was awarded a Queen’s Jubilee medal in 2003 and an outstanding achievement award from the Professional Pest Management Association of BC in 2005.

Follow Linda's work at­­­­­­­­­­­­­­­

May 26, 2017 11:46 AM

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