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Question:

What’s growing on the underside of my neighbor’s sunflower leaves?

Carl M., Los Lunas, NM

Answer:
At first, I thought the dusty black stuff looked like mold, but under a microscope, you can see that those black dots are a weird combination of eggs and insect poo (Fig. 1). I sent the leaf down to the NMSU Plant Diagnostic Clinic (http://aces.nmsu.edu/ces/plantclinic/). Here are comments from NMSU Extension Entomologist Dr. Carol Sutherland's diagnostic report: "These little creatures are 'lace bugs' (Order Hemiptera, Family Tingidae, Corythucha morrilli). The adult stage has the features that give these bugs their common name: lace bug. The elaborate pattern of veins in the wings looks like fine lace (Fig. 2). There are also structures on the thorax that continue the lacy pattern. As 'true bugs,' these insects have piercing-sucking mouthparts.

figure 1 rsFigure 1. Lace bug eggs laid on end and covered with frass
(photo credit NMSU Plant Diagnostic Clinic).
"They may feed on a variety of composite flowers, sunflower included. Sunflower leaves that seem a bit faded may be showing evidence of lace bug feeding by either nymphs or adults. When a nymph or adult takes a sap meal from the host, cells in the immediate vicinity are killed or injured. Since damage is cumulative, that accounts for that change in foliage appearance.

figure 2 rsFigure 2. Adult lace bug with characteristically lacy wings and thorax
(photo credit NMSU Plant Diagnostic Clinic).
"If you turn over enough sunflower leaves you can probably find different parts of the lace bug's life cycle. Each of their eggs is laid on end and often is covered with their feces (called 'frass'). They look like black 'stickers' on those leaves (Fig. 1). A little later, when the eggs hatch, the young nymphs are also black. With magnification, their bodies are quite spiny (Fig. 3). Only the adult stage has that fully developed lacework covering the wings and thorax.

figure 3 rsFigure 3. Lace bug nymphs are black with spines
(photo credit NMSU Plant Diagnostic Clinic).
"Severely infested leaves can shrivel, dry, and fall off, which may affect flowering and seed set in sunflower. If you're interested in protecting the plant from additional damage, you might look for some neem or azadirachtin products at the nursery; insecticidal soaps may be helpful as well as some of the light oil sprays (various vegetable oils). These products are available in organic forms (OMRI certified). They should be effective against both nymphs and adults if you direct your treatments toward the foliage and not the flowers."

I'm a sunflower fan for sure. Except for a few from South America, sunflowers (Helianthus spp.) are native to North America. The only trouble I have with sunflowers is how tired they look when the stalks bend over from the weight of the huge flowers. An Extension Master Gardener in Albuquerque once recommended planting sunflower seeds and morning glory seeds together. That way, towards the end of summer when the sunflowers are looking harried and spent, the slower-starting morning glories are ready to take off and use the sunflower stalks to climb and cover. It's a little messy-looking, but I love it. On his way to work in the summer mornings when I was growing up in Charleston, South Carolina, my Dad would take a "shortcut" to gaze at a wall of the bluest blue morning glories that turned magenta when wearing his sunglasses. Another way to outsmart sunflower sag is to stagger planting times so they don't all bloom (and then sag) at the same time.

In a discussion about the fun of growing sunflowers with Amos Arber (Xeriscape Inspector with the Albuquerque Bernalillo County Water Utility Authority), Sarah Hurteau (Albuquerque Urban Conservation Director at The Nature Conservancy), and Joran Viers (City Forester with City of Albuquerque Parks and Recreation Department), they were all three quick to point out the bird benefits. Lesser goldfinches and other birds love sunflower seeds straight from the source.

Most sunflowers are annuals, so seeds left over after the birds take their fill will reseed and come up next year as "volunteers." The Maximillian sunflower (Helianthus maximiliani) is a low-water-use perennial, so you can expect to see it up again and again each year with relatively little care. According to the USDA Plants Profile website (https://plants.usda.gov/), the New Mexico sunflower (Helianthus praetermissus) is the one that grows along highways across the state.

figure 4 rsFigure 4. Flowers bent at the flower base like this may have been caused by a head clipper weevil (photo credit M. Thompson).When I stepped outside to take photos of the sunflowers growing here at the NMSU Agricultural Science Center in Los Lunas for this column, I noticed several flowers were bent over at the base and turned black before they got full sized (Fig. 4). This is caused by aptly named head clipper weevils. I also noticed on other sunflowers in the garden that lower leaves were being munched on. I flipped a leaf and found dozens of bright orange, fuzzy caterpillars with black spines (Figs. 5 & 6), which may be the young form of the bordered patch butterfly or the Gorgone checkerspot butterfly (https://www.butterfliesandmoths.org/). I'll send a few of these cool critters down to Dr. Sutherland to find out for sure! But I'm not concerned about managing these "pests." Humans aren't the only ones who love sunflowers, and I'm okay with that. I planted enough seeds for all of us.

For more photos, a video of the caterpillars being sneaky, and links to information about different sunflowers and the animals that love them visit https://nmsudesertblooms.blogspot.com/
 
figure 5 rsFigure 5. Caterpillar and its droppings (photo credit M. Thompson).

figure 6 rsFigure 6. Caterpillar party on lower leaves of a sunflower grown from seed (photo credit M. Thompson).

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505-865-7340, ext. 113.