Southwest Yard and Garden

This column comes through the Grant County Extension Service out of New Mexico State University.

By guest contributor Dr. Gill Giese

powdery mildew evident on leaf top surface. giese copyPowdery mildew evident on leaf top surface is easier to see when leaf is turned “sideways” to catch light on infection sites that are in sporulation. Photo credit G. Giese.

Question: My husband and I are planting a few Marquette grape vines this year in Santa Fe. I would like to plant a tree approximately 8 feet from the vines. Could you recommend some trees that would be “a good idea” to plant close by? I read that planting a rose bush at the vines will help to indicate any diseases since the roses would get this first. Is this a good thing to do? Are rabbits a problem with grape vines? We have quite a few roaming freely. Should we protect the vines with a net around them?

with guest contributors Dr. Carol Sutherland and Dr. John Formby

pinon1Black specks on these older, browned piñon needles at a park in Albuquerque back in in March 2018 are a sign of a piñon needle scale infection. (Photo by M. Thompson.)

Question: I took these photos on one of the piñon trees nearest our house. We have thousands of piñon here on our land and our neighbor’s land, some of which have died within 12–14 days of turning brown. We would hate to see an epidemic, but it does seem to be spreading. What is it and what should we do?

- Paula P., Mora, NM (submitted via NMSU Extension Agent for Mora County, Suzanne DeVos-Cole)

silverleaf nightshade flower w 15Silverleaf nightshade flowers are beautiful, but these weeds are invasive and parts of the plant are toxic to humans and animals. Photo from NMSU Extension Guide “Silverleaf Nightshade” W-15.

By guest contributor Dr. Leslie Beck 

Question: Silverleaf nightshade and nutsedge are taking over parts of my yard! Please help. Organic control options are appreciated.

Helen B., Las Cruces, NM 

cenchrus sandburs and stalk photo from weeds.nmsu.edu 2

goatheads puncturevine photo from weeds.nmsu.edu

Both are annual weeds with vengeful, spiny seeds, but sandbur (top) is a grass and goatheads (bottom) are a flowering, broadleaf species. Photos from the NMSU website here.

Question: Can you help me battle my weeds organically? I’ve got sandspurs and goatheads. Are there soil conditions weeds hate?

Helen B., Las Cruces, NM 

Answer: Ouchie, that’s a nasty duo of weedy enemies. Most readers can commiserate all too well. Sandbur is a grass of the Cenchrus genus, also commonly referred to as “stickers” or “sandspurs.” Goatheads (Tribulus terrestris), also known as “puncturevine,” have tiny yellow flowers; delicate, compound leaves; and spiny seeds that are even meaner and tougher than sandburs. Many people mistakenly call sandburs “goatheads,” and I understand why. Both have spiny seeds. Both get all tangled in your socks and shoelaces when you’re not looking. Here’s the quickest way to tell the difference: place one of each seed type on the floor and then step on them both while barefoot. They both hurt, but pay attention to the depth of the pain and the length of time that pain persists. The goathead spines feel like they punctured all the way up to your knee and the spot of contact may ache for over an hour. You’re welcome.

Question: The Texas red oak, live oak, and pecan trees in my yard were looking bad going into the fall, as were my neighbor’s honey locust and maple. When I searched for problems online, I found different possible pests and diseases for each tree. Can you help me narrow down the possibilities?

Richard V., Hobbs, NM

Answer: This is Part II of the column on diagnosing tree problems. Last week, we learned that water stress and weed whacker injury are the most common tree problems in our landscapes, and that the rooting area necessary for large trees to survive and grow is much bigger than most folks realize.

southwestjanRed arrow is pointing to a porcupine munching on tree bark way up in the canopy of a cottonwood at the Albuquerque Botanical Garden in February 2018. (Photo credit M. Thompson)We also touched on the reasons why symptoms are rarely sufficient for conclusive diagnosis of a tree disorder. This is partly because symptoms may point to secondary or tertiary problems. Many—but not all—insect pests and pathogens are more likely to attack trees that are already stressed.

Plant stressors can be broadly divided into two categories: biotic and abiotic. Biotic stressors are caused by living or once-living organisms, like insects, bacterial and fungal pathogens, and animal pests.

Nature's Notebook is a national, online program with the USA National Phenology Network that uses amateur and professional naturalists to record plant and animal observations in a given location over time. The steps for becoming a volunteer are straightforward. And you can set your backyard as a location or pick a public space and get a group to sign up together (Visit Nature's Notebook here).

mulberry tree with girdled roots in torcGirdling roots on this mulberry tree in Truth or Consequences may be the underlying problem causing canopy dieback no matter how much extra water is applied. (Photo credit M. Thompson)Question: The Texas red oak, live oak, and pecan trees in my yard were looking bad going into the fall, as were my neighbor’s honey locust and maple. When I searched for problems online, I found different possible pests and diseases for each tree. Can you help me narrow down the possibilities?

Richard V., Hobbs, NM

Answer: Local tree experts agree that the number one tree “disease” in New Mexico is drought. And the number one pest for trees in New Mexico is humans with our weed whackers and mowers.

That being said, last summer over the phone with the Hidalgo County Extension Agent, I diagnosed Afghan pines with water stress. Luckily for those poor trees, I had a trip planned to visit Lordsburg that month, so we scheduled a site visit, and though the problem was technically water stress, it wasn’t what I expected. The homeowner’s soil was heavy clay, and the roots were staying way too wet.

Roots need water, that’s for certain. But it’s also true that they need oxygen, so before anyone waters their trees (along with all your other landscape plants), stick your finger in the soil or use a tool to dig down a few inches. If the soil feels moist, don’t water quite yet.

Roots also need space to grow. The rules differ by tree species and soil type, but the larger the tree trunk and canopy, generally, the larger the root zone needs to be. The International Society of Arboriculture defines the critical root zone (aka critical root radius) for a given tree as the area equal to a 1-foot radius from the trunk base for every 1 inch of trunk diameter. Trunk diameter measurements should be taken at 4.5 feet above ground (or thereabouts, depending on tree age and whether there are huge, knobby lumps in the trunk). As I mentioned back in June, the quickest way for me to estimate tree trunk girth without a measuring tape is to visualize a whole pizza that’s the same size as the trunk diameter—personal pan pizzas tend to be 6 inches and a large pizza is usually around 15 inches. So, if your tree trunk is a medium pizza size, you can guestimate that the trunk is 12 inches in diameter and translates to an approximate 12-foot rooting radius. That’s a 24-foot diameter of rooting area for a model tree to have room to breathe, but in order for the tree to continue to grow without failing, it will need even more space.

snowmeltTwo cups of snow scooped up from the front yard at the NMSU Agricultural Science Center at Los Lunas on January 3rd melted down to a little over 1/3 cup of water, but this isn’t always true because temperature has a big impact on snow density. Photo credit M. Thompson.

Question: We got 4 inches of snow just before the New Year that’s still melting a week later. I’m glad the established trees and shrubs are getting some water but is it enough to hold off on watering manually this month?

Joe S., Belen, NM 

Answer: There’s a rule of thumb that 10 inches of snow equals 1 inch of water, but it really depends on how wet the snow is, and that depends on temperature. Drier snow can be expected at lower temperatures and vice versa. I found some fun calculations and snowmelt discussions online. (Just like snow weight, fun is relative.) “In general, colder temperatures make snow fall less densely and lower the rain-to-snow ratio, resulting in more inches of snow per inch of rain… If 3 inches of rain are expected but the temperature drops suddenly to 5 degrees Fahrenheit, 120 inches of snow will fall” (Richard Graham, www.sciencing.com). That’s compared to 30 inches of snow required to get 3 inches of water when temperatures are close to freezing.

Until this past monsoon, I’d have said we’ll never expect 3 inches of rain on a single day in New Mexico. And I would have been wrong. On August 16, some areas of Doña Ana County got over 2.5 inches of rain. On July 24, more than 3.5 inches of rain was recorded in Santa Fe and Colfax Counties. Dr. Curtis Smith and I drove back down from Raton in that wild rainstorm. And some reported almost 4 inches of rain on August 24 in Grant County! When I searched back in previous years, there were lots of times when some lucky part of New Mexico got that much rain on a given day.

Question: I have a large monarch butterfly garden, and I gathered zinnia seed heads to plant next spring. Zinnia seeds appear to have two distinct morphologies. The ray flower seed is shield-shaped and the disk flower seed is smaller and flatter. Which of the seeds is viable? I have researched and found some who say only the ray seed, some say only the disk seed, and some say both. Please let me know which zinnia seed is most viable and why.

Tim P., New Mexico

swyg01Zinnia showing off both disk and ray flowers at the NMSU Agricultural Science Center in Los Lunas. Photo credit M. ThompsonAnswer: I know exactly what you mean. I’ve had this question before myself. Zinnias were one of my first garden successes when I moved to Las Cruces in 2009. I too gathered the seed heads and I too wondered which part was the true seed that should be saved. That year I just saved the whole shebang. In the late spring I crunched up the entire dried flowers and sprinkled them around the garden. It worked, so I kept that routine right up to today.