With the return of bees over the last week or two I am relieved to see them once again working garden flowers. Every year I get concerned inquiries in May asking where the bees are. While insect populations, including native bees, have been steadily decreasing over recent decades, a marked absence of bees for several weeks in spring is usually because the bees are working on tree flowers or have found a patch of more attractive plants elsewhere. Bees really like maple flowers and later on Arbutus/Madrone flowers. In my neighbourhood, both of these trees lure bees high above our heads and it is only after trees are done blooming that we see good numbers of bees back in our yards.

The cool (even cold!) weather of the last week or so has been pretty hard on tender vegetables planted early, such as tomatoes, beans, peppers, cucumbers. With the weather warming up and higher overnight temperatures expected by this weekend, plants should recover. Depending on how protected your garden is, however, there may have been some damage to tender leaves from cold winds. Damage looks like dry or wilted, white or tan areas on leaves, or possibly whole leaves. While the damaged leaf area won’t recover, if plants continue to grow healthy new leaves and shoots, they should be OK. If the stems have collapsed, however, replanting will be necessary. Despite the weather, lots of vegetables have been thriving: broccoli, cauliflower, cabbage, chard, lettuce and salad greens, onions, potatoes, root crops. In my garden, even zucchini and other squash have been able to handle the weather (Permit me a brief brag: This year I set a personal best for early zucchini when I picked a 20 cm/8 in zucchini on May 5. It was started weeks earlier than I sow other squash and was nursed along in my greenhouse until it was planted out in late April. You really have to like zucchini to bother with all that!)

Vegetable Pests: Below is information on 3 common insect problems that appear to be top of mind for many gardeners this month. But first, for any pests on plants it is important to keep in mind that most pests (and pathogens, too) only attack particular host plants. While there is the odd exception, most insects only feed on certain plants. They cannot eat other, unrelated plants even when their host plant isn’t available. For example, cabbage root maggot and carrot rust fly are very similar, but one feeds only on roots of Brassica (mustard/cabbage) family plants, while the other only attacks Carrot Family plants. Even aphids, of which there are many different species, are particular. The aphids causing plum leaves to curl up right now won’t move to other kinds of trees and the same applies to apple aphids, maple aphids, rose aphids, bean aphids, cabbage aphids and others. A pest infestation on one kind of plant doesn’t mean that unrelated plants are in jeopardy. Photos of the insects described below can be seen on my website under the Pest & Disease Images menu: the first 2 insects are under “Root Feeding Insects”, while the leafminers are under “Other Leaf Chewing Insects”

Carrot rust fly: A small fly that attacks plants in the carrot family (including parsnips, parsley, dill, cilantro), they lay eggs where the stems of plants emerge from the soil. After the eggs hatch, tiny white maggot burrow into the roots. There are 2 to 3 generations over the season, with the last generation in late summer the most numerous and damaging to overwintering carrots. Covering carrot beds with insect netting or floating row cover (main image) before seeds germinate, prevents the flies from laying eggs and results in a pest-free harvest.

Cabbage root maggot: Very similar to carrot rust fly in life cycles and behaviour, but this small fly only lays eggs on cabbage, broccoli, cauliflower, radishes and other plants in the Brassica Family. Covering seed beds before germination with insect netting or floating row cover entirely prevents plants from being attacked, however, is workable only for small plants, such as radishes and leafy greens, or for young seedlings of plants that eventually become very large (broccoli, cabbage, Brussels sprouts, etc.). For large plants, another type of barrier works well. At transplanting time or when plants have outgrown insect netting, slip a barrier around the stem of each plant. Make the barriers (a friend calls them ‘diapers’) out of any soft, waterproof, flexible material, such as freezer paper or recycled plastic, such as from bags of compost. Cut a 15 cm/6 in square of material, then cut a slit to the centre of the square. Slide the barrier around the seedling stem so that the material lies flat on the soil with a tight fit to the stem. The flies only lay eggs in the soil beside the stem and not further away so this barrier prevents that. Make sure the barrier stays flat on the soil so insects can’t walk under a turned-up edge (I use a couple of small pebbles to keep it down) and later, mulch right over the barrier and leave it in place for the life of the plant.

Cabbage root maggot barriers

Beet/spinach leafminer: Brownish blotches on leaves are caused by a fly that lays its eggs on the underside of leaves of beets, chard, spinach, sorrel and sometimes rhubarb. When the eggs hatch, tiny maggots burrow between the upper and lower surface of the leaf. There are 2 or 3 generations over the summer. Though often there isn’t much damage from the early generation, damage from later generation can be quite serious. Right now, look for tiny chalk white eggs laid on the undersides of leaves and either brush off the eggs or harvest the leaves, wash off the eggs and use the leaves as usual (that eliminates eggs that would become the next generation). If there was a lot of damage last year, this year prevent attack by covering seed beds with insect netting or floating row cover before the plants come up.

Beet leafminer damage

Using insect barriers: For all 3 pests above, the most effective control is to prevent the adult flies from reaching plants to lay eggs. Many brands of insect netting are now sold (e.g., ProtekNet, Environmesh, BugOut and others) and you can also use floating row cover fabric. It is cheaper and lighter weight so does not need to be supported above the plants, but is not as durable as the insect nettings, which are very sturdy and last for years. Support insect netting above plants on wooden corner stakes or over hoops of some kind. To be effective, barriers must be in place before the plants attract the flies, which means covering seed beds before seedlings come up or covering starts the same day they are set out in the garden. Covers must not have holes in them and the edges should be held down in tight contact with the soil so there are no gaps for insects to crawl under the netting. I use 1x2 scraps of wood and stones to hold down my covers. Covers have to stay in place for the life of the plants or until late October for overwintering crops, but you can lift the covers during the day to weed, thin and harvest. The adult insects fly at dusk so as long as you replace the covers when you are done working in the crop, there is little risk that a fly will zip in and lay eggs on exposed plants.

Recycling Corner: Rather than rewriting information from previous newsletters, I refer you to timely notes in the archive on my website.

--See May 27, 2024: Sowing winter crops, ABCs of Gardening: Irrigation: Especially note what to sow by the end of May for harvest next winter (I can’t believe we are already planting for winter (!) but there are few crops that take all season to grow and they do need to started now.

Upcoming talk open to the public:

Saturday May 31: 1:00-3:00 pm. Bugs in the Garden: The Good, the Bad, and the Merely Ugly. Online via Zoom. When it comes to insects in your garden, do you know how to tell pests from beneficial species? Afterall, most of the insects in gardens are not pests. All too often, plant damage is blamed on good bugs found on leaves where they are actually hunting for the true culprits. This talk will show you how to distinguish common beneficial insects from pests and will review ways to manage pests while causing the least harm to beneficial insects. Sponsored by the Compost Education Centre in Victoria. To register: https://compost.bc.ca/get-involved/public-workshops/