Trials of Indoor Gardening pt.1: spider mites, aphids, and thrips oh my...

Posted by: John Stolzle, Jefferson County Extension

One of the best things about indoor gardening is being surrounded by green foliage during winter. But this also brings a potential for pests to thrive 365 days a year.

The indoor garden remains unaffected by an early season blizzard; fresh produce as of this publication date!

One of the greatest challenges my garden has faced has been a battle against aphids and spider mites. In outdoor environments, natural predators do much to keep populations of pests (like aphids and spider mites) in check. But in the climate-controlled world of an indoor garden or greenhouse pests can reproduce unchecked by predators and lead to imbalanced (aka. out of control!) populations.

Where did they come from?
With a few exceptions, plants which I started from seed have remain unscathed; however, a few plants which were placed next to incoming nursery stock encountered problems.

Damage from inadequate watering and spider mites on a Jalapeño

Case in Point: one poor Jalapeño (photo above) that was started from seed caught a bad case of spider mites from another pepper plant which was purchased from a commercial nursery/greenhouse. Initially things in the garden were great but while I went away on vacation, insects were busy chowing down on my pepper plants. I returned to what you see in the picture.

Some time after this, I purchased a sad looking (#discount) Taro plant. I placed it in the garden, wiped off its leaves and stalks with a damp paper towel, and watched it closely. After some weeks, I began to notice many tiny glistening, sticky spots on its leaves; the spots were honeydew, evidence (waste) left by aphids. I took a closer look (picture below) and saw tiny green insects (aphids) moving around the leaves.

Aphids on a Taro leaf

A lack of patience.
One pepper which had become infested with spider mites appeared to stop growing after treatment. I became frustrated because it hadn’t produced a new leaf over the course of two months! So, I decided to rip out the pepper and use the pot for something else.

Pepper plant after 3 months of growth in an 18cm (7in) diameter pot.

Little had I known that the plant had been developing a very robust root system. Sigh.. a root system that would have been able to support many specialty peppers. On the flip side, now I know the plants are growing and that this container was likely too small for the plant anyway. Recommendations for adequate container sizes can be found here: https://cmg.extension.colostate.edu/Gardennotes/724.pdf

What can be done... aside from tearing out a plant?

It is important to first know what may be attacking a plant. For example, after looking for some time (phone cameras, magnifying glasses, hand lenses, and microscopes can be helpful!) I observed not only spider mites but also thrips on my pepper plants! These two insects require slightly different management strategies. Note: Information on thrips is linked-to at the end of this post.

Spider mites and aphids lay eggs on plant material and go through a roughly 2-week life cycle (important to know when planning follow-up treatments). A jet of water is often enough to dislodge these pests from many plants. Have a spider plant (‘Chlorophytum comosum’) with spider mite webbing between its leaves? - Give it a shower in the sink!

It is easier to battle 10 insects than it is 10,000. Washing a nursery plant upon its arrival can save headaches  by preventing major outbreaks from ever occurring. Note: Not all plants like to have wet leaves. It can be helpful to look up a plant’s general care recommendations.

Insecticide products do exist for treating spider mites, aphids, thrips, and other various plant pests. Insecticidal Soaps with the active ingredient Potassium Salts of Fatty Acids, and Horticulture Oils (e.g. Neem, Cottonseed) can be effective parts of an integrated pest management strategy. It may not seem like it, but Insecticidal Soaps and Horticultural Oils can be harmful to humans and pets and other non-target organisms. Pesticide product labels should always closely be followed and adhered to. Note: when applying an insecticidal soap (active ingredient: 'Potassium Salts of Fatty Acids') any insect not completely wetted (e.g. an aphid hidden in a rolled up leaf) will not be affected.

What I wish I would have known.

• That placing plants in the shower or sink or (even better!) taking them outdoors prior to treatment can make cleanup a much easier process.
• Some plants can react poorly to Insecticidal Soap and/or Horticultural Oil treatments. It can be mildly traumatic to see a plant drastically defoliate a day after being treated.
• Yellow sticky pads can be incredibly effective at managing indoor populations of fungus gnats (sometimes mistakenly referred to as fruit flies).
• Patience is key (in reference to the pepper I tore out).

For more information on a variety of topics, please see the links, below.

• More info on managing Houseplant Pests: https://extension.colostate.edu/docs/pubs/insect/05595.pdf
• Insect Control: Soaps and Detergents: https://extension.colostate.edu/docs/pubs/insect/05547.pdf
• Insect Control: Horticultural Oils: https://extension.colostate.edu/docs/pubs/insect/05569.pdf
• Spider mites: https://extension.colostate.edu/docs/pubs/insect/05507.pdf
• Fungus Gnats: https://extension.colostate.edu/docs/pubs/insect/05584.pdf
• Thrips lifecycle: http://ipm.ifas.ufl.edu/applying/Biology_of_Thrips.shtml
• Western Colorado Thrips: http://www.wci.colostate.edu/shtml/ot.vs.wft.shtml

As a fun aside, insects (like 'Lady Bug' and Lacewing larvae) which feed on spider mites, aphids, etc. can be purchase from locations around the USA. Here is a very impressive list of BioControls and example locations from across the US where they can be acquired: https://webdoc.agsci.colostate.edu/bspm/InsectInformation/Factsheets/BioControlSuppliers.pdf

For an introduction to this indoor garden, please see this blog post: https://csuhort.blogspot.com/2019/09/reflections-on-season-of-indoor.html

 Best of Luck in all your gardening endeavors! 
- John 

Spiders in the Garden

Posted by: Jessica Wong, Master Gardener Coordinator, Broomfield County Extension

Spiders may be one of the most important and abundant biological control agents in our gardens. They are generalist predators that feed almost exclusively on arthropods, including many we consider pests. Spiders will kill as many as 50 times the number of prey they actually eat. And, relax, they are not at all interested in biting humans.

This female wolf spider (Tigrosa helluo) was recently brought into our office by a Broomfield employee. She was about 3 inches long! I released her into our Xeriscape Demonstration Garden where, I'm sure, she is providing effective pest control. Photo credit: Jessica Wong 

Dysdera crocata, commonly known as sowbug killer, woodlouse hunter, and “roly-poly killer.” Photo credit: iNaturalist.org

Spiders provide pest control, day and night, on the ground, on all above-ground parts of a plant, and even in the air. Wolf spiders (Lycosidae) are excellent hunters of pests on the ground, including ants, earwigs, and caterpillars and grubs found at the soil surface. Sowbug killers (Dysdera crocata) are another ground hunting spider that prey on, you guessed it, sowbugs and pillbugs.

This spider is aptly named bold jumper Phidippus audax. Photo credit: Jessica Wong

Jumping spiders (Salticidae) are small hunters can be found in a variety of habitats, from tree trunks to leaves to under rocks. These small spiders hunt for small prey like mosquitoes, aphids, and midges. Crab spiders (Thomisidae) are ambush predators that can be found waiting for prey on flowers. Orbweavers (Araneidae) are the spiders that spin the familiar vertical webs with concentric rings. They catch anything that flies by, such as winged aphids, wasps, and moths.

Goldenrod crab spiders Misumena vatia can change from white to yellow and back to white for better camouflage. Photo credit: Charley Eiseman, Ohio State University Extension

Banded orb weaver Argiope trifasciata. Photo credit: David Cappaert, Michigan State University, Bugwood.org

Spiders can provide the most effective pest control when there are many species present in your garden. To support spiders in your garden you will need to provide habitats for them. Apply a layer of mulch or leaf litter for the ground spiders. Reduce tilling to prevent the disturbance of spider nests and burrows. Intercrop varying height plants to create microclimates and web anchor points. Diversifying your landscape can increase the diversity and abundance of spiders in your garden, which will increase the potential for pest control. By creating abundant habitat for spiders in your garden you will also make it more attractive for them to stay outside rather than come inside your house.

Various groups of spiders occupy different parts of a tree. Figure from Patrick Marc & Alain Canard 1997 “Maintaining spider biodiversity in agroecosystems as a tool in pest control.” Agriculture, Ecosystems and Environment 62:229-235.

I love spiders. Spiders are always welcomed in my garden. I don’t even mind them in my house since they are doing a great job of killing flies and ants. I don’t expect you to love spiders now too, but I hope you at least have a greater appreciation for them in your garden.

Coffee with a little IPM

Posted by: Mary Small

Colorado Master Gardener Program Coordinator

One of the topics I teach in our Colorado Master Gardener program is Integrated Pest Management or IPM. It’s a multi-prong approach to managing pests and can be used in a variety of situations. I wrote about how I used IPM strategies to combat fruit flies in the kitchen last fall. Here’s another story.

Last year at this time, I was in Guatemala on a mission trip. On our free day, a group of us toured a coffee plantation near Antigua, situated at about 5,000 ft in the western highlands.  We were looking forward to the tour and sampling their product at the end.

And then…..as we wandered down a row of coffee plants, I became distracted when our guide pointed out rust disease on some leaves.  I just had to have a picture! (If you know me, this is no surprise. I like “weird stuff” as my children often have reminded me.)

Rust on coffee leaf

While I was angling for a good shot, the guide told us about the plantations’ disease management strategies.  Their practice was to treat only the plants that had the disease rather than treating the whole crop. Before they treated, they watched the outbreak areas to determine if sprays were really needed. Sometimes they were, sometimes not. In IPM, this is known as “spot treatment”. The purpose of a spot treatment is to minimize pesticide exposure of non target organisms as well as control costs. And this is done by only treating what is necessary – when it is necessary and according to specific threshold levels of the pest.

Trees shading coffee

One of our group asked about the large trees growing among the coffee plants. Why were they there? Didn’t that keep light from reaching the leaves and berries? Well, yes, it did. The light intensity is so high that it “sunburns” the coffee fruit, rendering it useless for the beverage market. The trees are there to decrease the incidence of berry burn. This is an example of a cultural IPM practice – altering the culture (manipulating the environment) to reduce the likelihood of “pest” (read: sun) damage.

Trees with fruit to attract birds

Our guide also pointed out newer trees (whose name escapes me) that were planted with a purpose. One of the plantation’s ongoing problems was birds swooping down into the coffee crop and taking the fruit. (If you raise anything that produces fruit, you can understand the frustration here!) The company tried different strategies until they learned this tree produces fruit that the birds really like. So the tree fruit acts to divert them from the desired coffee crop. Nothing is 100%, but it was more successful than anything else they previously tried. In IPM, we would call this trap cropping. (Think planting radishes to attract the western cabbage flea beetle, so they won’t decimate the broccoli.)

 Now, having raised fruit bearing plants, I’ve since pondered what happens when the birds “re-sow” the seeds of the tree fruit with a little bit of their fertilizer. Didn’t think of it. Too distracted by the wonders of viewing IPM in practice…and fresh-ground Guatemalan coffee!