"News You Can Use"
Bacterial Leaf Spot Affecting Pumpkins Statewide
Over the past month, the New Mexico State University Plant Diagnostic Clinic has received several pumpkin samples with classic symptoms of bacterial leaf spot. This disease was identified last year in one county in NM. So far this year, three counties - Luna, Curry and San Juan - are positive for the disease. Symptomatic fruit exhibits small, round, slightly sunken spots with tan to beige centers. Overtime, spots enlarge, becoming noticeably sunken, and the rind cracks in the center of the lesion. Inside, the flesh is rotted all the way to the seed cavity. When cultured for disease agents, pure cultures of Xanthomonas campestris pv. cucurbitae, the causal agent of bacterial leaf spot, has been isolated from all symptomatic fruit. This disease causes sporadic losses in cucurbit crops grown in temperate climates. Disease occurs when warm, humid conditions are persistent. The disease attacks a number of different hosts including pumpkin, cucumber, gourds, and summer and winter squash. More information about this disease can be obtained from the Bacterial Leaf Spot of Cucurbits Fact Sheet. Contact: Natalie Goldberg
Fairy Ring in Lawns
Finally! Rain! Oh, how badly New Mexico needs rain. But with the good....well, you know, can come the bad. Heavy September rains have created a perfect environment for mushroom forming fungi. Some of them are harmless - interesting or scary looking (see News You Can Use item below) - and some of them are plant disease causing agents, such as the fairy ring fungi. Fairy ring is a disease of turfgrass, which can result in rings of dead grass, and under conditions of significant moisture, produces mushrooms, toadstools or puffballs in circles. The disease can be caused by several different species of soil-inhabiting fungi in the fungal group (class) known as basidiomycetes. All grass species are susceptible to this disease.
Symptoms of fairy ring are variable depending on the fungal species, soil type, condition of the grass, and the environment, but generally consist of circles or semi-circles in the affected turf area. The disease may appear as circles, rings or arcs of dark green, faster growing grass. The grass inside the rings may die-out leaving dead areas surrounded by dark green growth or the rings may develop with no dead grass (surrounded by normal colored grass). Conversely, some fairy ring fungi result in circles or arcs of dead grass surrounded by apparently healthy grass. Rings can vary in size during the year and can appear or disappear throughout the growing season. The rings may be surrounded by mushrooms, toadstools, or puffballs which are fruiting bodies of these fungi. In some cases, rings of fruiting bodies may develop with no visible effect on the grass. These fruiting bodies are excellent signs of the fungi and can be used as a diagnostic tool. Weed invasion into affected areas is common due to the lack of competition from healthy grass. Some fairy ring fungi cause a hardened hydrophobic (water repellant) layer to develop resulting in turf areas that are difficult to water. Check out the Fairy Ring Fact Sheet for more information on this disease. Contact: Natalie Goldberg
Heavy Summer Rain Creates Perfect Conditions for Stinkhorn Fungus
What a surprise! Visit your garden and see this ominous, stinky, weird looking mushroom. Alarming? It could be. Until you know what it is....this mushroom is the fruiting body of Mutinus elegans, a fungus commonly known as the elegant stinkhorn, the headless stinkhorn, or the devil's dipstick (Mutinus caninus, the dog stinkhorn, is a very similar species). Colorful? Yes, in both appearance and name! This saprophyte is harmless to plants, but can be a shocking discovery in your garden. This fungus is typically found growing on the ground by itself or in small groups on woody debris or leaf litter, during summer and fall. It likes rich soils and plenty of moisture. In North America, it is most common east of the Rocky Mountains, but is occasionally found in the Western U.S.
The fruiting body begins its development in an "egg" form, resembling a "puffball" partially submerged in the ground. As the fruiting body matures, a slender orange to pink colored stalk emerges that tapers evenly to a pointed tip. The stalk is covered with a foul-smelling slimy green spore mass on the upper third of its length. Insects, particularly flies, feed upon the slime which contains the spores. The spores adhere to the insect's body and the insect serves as a vector (disseminating agent) to move spores from one location to another. Due to their repellent odor, mature specimens are not edible. In the laboratory, Mutinus elegans has been shown to inhibit the growth of several microorganisms that can be pathogenic to humans. Click here for more photos. Contact: Natalie Goldberg
Dodder, a Parasitic Plant, is Appearing Across the State
Environmental conditions across the state are perfect for the parasitic weed, dodder, to germinate and grow. This parasite does not have leaves and cannot produce chlorophyll. As such, it grows on other plants, using them for water, nutrients, and carbohydrates. It is common along road sides, but can also grow on crop and landscape plants. In the spring, dodder seeds germinate near the soil surface and send up slender, thread-like twining stems varying in color from pale green to yellow or orange and without any cotyledons (seed leaves). The slender, leafless, thread-like stem sways or rotates slowly until it touches the stem or leaf of another plant and begins to wind around it. On a host plant, the dodder stem will immediately form small appendages called haustoria (tiny sucker-like roots), which penetrate the stems or leaves so that dodder can extract its necessary growth requirements. Soon after attaching to a host plant, the lower end of the dodder withers and breaks its connection with the ground, while the upper part of the stem grows rapidly, often forming dense stringy masses. However, if the dodder seedlings are unable to contact a susceptible host plant soon after germination, they will not survive. The damage of dodder to the host plant varies from moderate to severe depending on the growth of the host plant and on the number of haustoria attachments to the host plant. Dodder infestations reduce crop yield and increase harvesting costs for crops like alfalfa. For more information, please see the Extension publication Dodder (Cuscuta spp.), Biology and Management. Contact: Natalie Goldberg or Jamshid Ashigh
Bacterial Leaf Scorch Evident on Chitalpa Trees
The Heat of Summer brings on Symptoms of Bacterial Leaf Scorch Symptoms on Chitalpa - Chitalpa trees (a hybrid between catalpa and desert willow) are susceptible to a xylem-limited bacterium called Xylella fastidiosa. The bacterium invades the plant and plugs up the water conducting vessels, known as the xylem vessels, making it difficult for the plant to get enough water to the leaves. The result on the plant is symptoms of water and nutrient stress - chlorosis and leaf scorch. Other symptoms include leaf spotting, small leaves, thin canopy, branch dieback, and eventually, tree death. This disease was first discovered in New Mexico in 2006. The disease was also confirmed in grapes the same year. In grapes, the disease is known as Pierce's Disease. In 2010, the disease was also confirmed in catalpa and peach.
The disease is transmitted from one plant to another through xylem-feeding insects, most notably sharpshooters. While New Mexico has some native sharpshooters, the most efficient vectors for Xylella, the glassy-winged sharpshooter and the smoke-tree sharpshooter, are not known to occur. Still, research at New Mexico State University has shown that the bacterium is nearly identical in chitalpa, grape and catalpa. This indicates transmission, probably by native sharpshooters, between these hosts. Research has also shown that nearly all chitalpa trees are infected with this bacterium. The disease is particularly common in chitalpa because this hybrid is vegetatively propagated. When an infected mother plant is used for cuttings, the newly propagated plants will be infected.
Unfortunately, there is no cure for plants infected with the bacterium. Reducing plant stress by making sure the plants are adequately watered and fertilized will help to reduce the impact of the disease on the plant and may prolong the life of infected trees. Pruning out dead and dying limbs will also help to improve the appearance of the plant. Ultimately, however, infected plants will become unsightly and will die if they are not removed from the landscape. Click here for more photos of this disease. Click here to view a PowerPoint presentation on this disease. Contact: Natalie Goldberg
NMSU's Extension Plant Sciences Department to Bring Plant Clinic to Farmers' Markets
New Mexico State University's Extension Plant Sciences department will host a Plant Clinic at several farmers' markets this summer, beginning July 13 in Las Cruces, to help educate the community about horticultural practices and pest management, including identification of insect, weed, and disease problems.
"We encourage anyone who is interested in gardening and has a question that they have not been able to get answered, to come out and visit with us," said Natalie Goldberg, department head of NMSU's Extension Plant Sciences. "If they have problem plants or pests that they would like to identify, they are encouraged to bring us a sample of the plant or pest."
The question-and-answer sessions will be hosted by three specialists: Carol Sutherland, entomologist; Jason French, an expert on plant disease and diagnostics; and Goldberg, who is an expert on plant diseases and disorders. In addition, the county Extension agent will be available to help answer questions about horticulture.
"Some problems people bring to the clinic might be resolved on the spot, but others might need more background information to complete an answer, so we'll make sure we have the client's contact information and specific question written down so we can contact them later," said Sutherland, who will have a collection of insects on display for additional questions.
Goldberg added they hope to answer most questions but if they can't, they will either take back samples for further research or connect clients with other experts.
"Plant Clinics are a great way to interact with people not familiar with the great variety of information available through the Cooperative Extension Service," Sutherland said.
Plant Clinic schedule:
- July 13, Las Cruces, Las Cruces Farmers' Market, 8 to 10 a.m.
- July 24, Deming, Copper Street Farmers' Market, 8 to 10 a.m.
- July 24, Alamogordo, Alameda Park Farmers' Market, 5 to 7 p.m.
- July 31, Taos, Taos Pueblo Red Willow Farmers' Market, 10 to noon
- July 31, Albuquerque, Cedar Crest Farmers' Market, 3 to 5 p.m.
- Aug. 1, Los Alamos, Los Alamos Farmers' Market, 7 to 9 a.m.
For more information on the Plant Clinics, contact Natalie Goldberg
Iron Chlorosis Takes its Toll on Landscape Plants
Iron chlorosis takes its toll on landscape plants - It seems early for the 'dog days of summer,' but already, many of our landscape plants are showing symptoms of environmental stresses common during the hot, dry summers. One of the most common landscape disorders in New Mexico is iron deficiency, also called iron chlorosis. Iron deficiency symptoms typically begin in spring when the plants are leafing out. As summer progresses, untreated plants may exhibit severe symptoms and have an overall unthrifty appearance. Samples from these plants are often submitted to the NMSU Plant Diagnostic Clinic because growers are concerned that there is a disease agent involved. In most cases, the plants are suffering only from iron deficiency either by itself or combined with other environmental stresses, such as water stress, hot drying winds, and other nutrient deficiencies.
Iron Deficiency is one of the most common nutrient deficiencies in all sorts of landscape plants. Some of the most commonly submitted plants for diagnosis include: Photinia, willows, mulberry, maples, sycamore, Poplars, roses, apples, pears, Hawthorne, stone fruits and pecan. Iron is a critical element for good growth and green color. Iron may be plentiful in the soil, but it is tightly bound to the soil particles in high pH (alkaline and calcareous) soils. Under these conditions, the iron is unavailable for plant use. The classic symptom of iron deficiency is interveinal chlorosis where the leaf turns yellow and the veins remain green (Fig. 1). In very severe cases, leaves may turn white in color or develop necrotic spots, which can look like a fungal infection, on the affected leaves. Over time, plants which remain untreated will start to dieback (Fig. 2), become unsightly in appearance and may eventually die. More information on this disorder and it's management can be found on the Iron Chlorosis Fact Sheet. Contact: Natalie Goldberg or Jason French
Fungal Diseases of Roses
Fungal diseases on roses begin as spring turns to summer - Roses, one of the most common landscape flowering shrubs, can be beautiful with lush green foliage and brightly colored flowers. Unfortunately, they are also vulnerable to a couple of very common fungal diseases, powdery mildew and black spot, which can turn plants slightly in a short period of time. Black spot is specific roses, but powdery mildew can occur on a wide range of landscape plants. As such, you may see disease on your roses, bedding plants, and turfgrass all at the same time. The specific fungus causing disease on each of these plants is actually a different fungal species, but the environmental conditions that favor disease is similar and plants may become infected at the same time of year.
Black spot requires leaves to be wet for several hours in order for spore germination and infection to begin. Secondary spread of the disease occurs when spores are splashed from infected leaves to uninfected leaves by rain or sprinkler irrigation. Powdery mildew, on the other hand, doesn't require free water on the leaf surface, but does require high humidity for spore germination and infection. Cultural practices reduce leaf wetness and humidity can be helpful in managing these diseases. For example, it is best to avoid wetting the leaves when irrigating. If this isn't possible, then plants should be watered early in the day so that the leaves dry quickly. Additionally, planting in sunny locations with good air circulation, avoiding overcrowding, and selectively pruning plants to open the plant canopy, will help reduce disease. When planting new roses, select disease resistant cultivars. Good fall sanitation practices are also important for an overall disease management program - rake and destroy fallen leaves (do not compost diseased plant material) and prune out infected canes. Lastly, many fungicides are available to help control these diseases. For best results, use early in the disease cycle before symptoms are too widespread or severe and be sure to completely cover the plant including the upper and lower leave surfaces. Contact: Natalie Goldberg
Loose Smut of Wheat
Have you seen dark black seed heads on your wheat? If so, your plants may be infected with the fungus, Ustilago tritici. The disease is commonly referred to as loose smut of wheat. This disease has been known for centuries and is easy to recognize in the field. The disease appears at heading when dark brown to black, smutted, seed heads appear among newly emerged, healthy, green heads. The seed in these diseased heads are converted into a mass of dry, dark brown to black spores (teliospores). The disease is called loose smut because the spores produced on smutted heads are easily removed by wind and rain. Typically, after a short while, only the bare, sooty, flower stocks remain. In some cases, the seed head is only partially infected. Prior to heading, diseased plants may have dark green leaves with chlorotic streaks, but this symptom generally goes unnoticed. Seed with no visible symptoms can be infected with the fungus. Loose smut occurs worldwide. It reduces yield in proportion to the percentage of "smutted" heads. Although yield losses are usually less than 1%, losses closer to30% can occur under conditions that are especially favorable for disease development. In contrast to other wheat seed diseases, loose smut has little to no effect on grain quality for food or feed. More information on loose smut of wheat can be found on the Loose Smut Fact Sheet. Contact: Natalie Goldberg
Black Rot on Butternut Squash
At the end of October, a butternut squash with classic symptoms on black rot was submitted to the NMSU-Plant Diagnostic Clinic or disease analysis. The fruit was incubated in a moist chamber and a few days later, Didymella bryoniae, was sporulating on the surface of the fruit. This pathogen is the causal agent of black rot. It is also the causal agent of gummy stem blight, a devastating disease of cucurbits in the field. Yield loss occurs from both pre-harvest and post-harvest losses. As a fruit rotting pathogen, Didymella bryoniae can be particularly damaging to winter squash (butternut, acorn, buttercup, hubbard, etc.) and pumpkins. Other cucurbits such as watermelon, cucumber, and grounds are also affected. The disease occurs worldwide in tropical, subtropical and temperate climates. It has also been reported in greenhouse production. More information about this disease can be obtained from the Black Rot of Cucurbits Fact Sheet. Contact: Natalie Goldberg
Bacterial Leaf Spot Affecting Pumpkins in New Mexico and Texas
Recently, pumpkins from two different fields, one in New Mexico and one in Texas, were submitted to the New Mexico State University Plant Diagnostic Clinic for disease analysis. The fruit was exhibiting small, round, slightly sunken spots with tan to beige centers. On one of the fruits, spots were enlarging, becoming noticeably sunken, and the rind was cracked in the center of the lesion. Inside, the flesh was rotted all the way to the seed cavity. Infected tissue was plated for fungal and bacterial pathogens. No fungal pathogens were isolated, but pure cultures of Xanthomonas campestris pv. cucurbitae, the causal agent of bacterial leaf spot, were isolated from fruit from both fields. This disease causes sporadic losses in cucurbit crops grown in temperate climates. In New Mexico, the disease is not common, but can occur when warm, humid conditions are persistent. The disease attacks a number of different hosts including pumpkin, cucumber, gourds, and summer and winter squash. More information about this disease can be obtained from the Bacterial Leaf Spot of Cucurbits Fact Sheet. Contact: Natalie Goldberg
Alfalfa Mosaic Virus on Peppers
Over the past month, the New Mexico State University - Plant Diagnostic Clinic has received several plant samples that are exhibiting severe symptoms of Alfalfa Mosaic Virus (AMV). This virus is found worldwide on a wide variety of cultivated plants and weed species, and is particularly common on plants in the solanaceous (nightshade) and leguminaceous (pea) plant families. It is common in New Mexico on chile peppers and has also been identified on tomato, bean, alfalfa, peanut, cowpea and lavender. While this disease occurs every year in New Mexico, it rarely causes serious economic losses as the number of plants infected in any given field is usually low. It can, however, severely infect individual plants resulting in little of no fruit production. Symptoms caused by Alfalfa Mosaic Virus can be somewhat varied, but the most common symptom is white to yellow blotches in a mosaic pattern on the leaves. Other symptoms seen in peppers include white discoloration that occurs in a ringspot or curving mosaic pattern. When young plants are infected, they are stunted and produce small, deformed fruit. When mature plants are infected, the fruit produced before infection is normal, but little or no fruit is produced after infection. More information on this disease can be obtained from the Alfalfa Mosaic Virus Fact Sheet. Contact: Natalie Goldberg
Pink Root on Onions
Are your onions smaller than you'd like? Do the roots have a reddish-purple hue? If you answered yes to these questions, than your plants are suffering from a fungal disease known as pink root. Pink root on onions is caused by the soil-borne fungus Phoma terresstris. This pathogen is common in New Mexico and is problematic worldwide wherever onions are grown. The disease is especially devastating in warmer climates. Although many isolates of this fungus are specific to onion, some have the ability to infect other hosts including tomatoes, soybean, eggplant, pepper, spinach, carrots, corn, small grains, cucurbits, corn and ryegrass. The most noticeable symptom of the disease is the reddish-purple discoloration that occurs on infected roots (Figure 1). Roots of infected plants become dysfunctional and plants will suffer from nutrient deficiency and drought. When young seedlings are infected, they may die; however, death is not the end result when more mature plants are infected. In this case, plants are stunted, exhibit leaf tip dieback and bulb size is reduced affecting overall yield and marketability. More information on this disease can be obtained from the pink root fact sheet. Contact: Natalie Goldberg
Entomosporium leaf spot
If you've noticed reddish purple spots on the leaves of your indian hawthorne or red tip photinia, your plants are most likely infected with a fungal disease known as Entomosporium leaf spot. This disease is common on plants in the rose (rosaceae) family, but is particularly problematic on indian hawthorne (Raphiolepis indica) and red tip photinia (Photinia fraseri). The disease is especially troublesome in locations were cool, wet springtime conditions prevail. In New Mexico, the conditions that favor disease development do not last very long. As such, this disease is usually fairly mild on plants grown in New Mexico. When infection is low or mild, the damage is cosmetic - the plants don't look good, but the overall health of the plant is not affected. The overall health of plants with severe infections is negatively affected. Heavily infected plants may prematurely defoliate weakening them to environmental stress, insects and other diseases. More information on this disease can be obtained from the Entomosporium fact sheet. Contact: Natalie Goldberg
Common Corn Smut
Common Smut Appearing in Corn Fields across the State - If you have noticed swollen, blackish-blue, kernels on your corn ears, you are not alone. Over the last few weeks, common smut has been appearing in corn fields across New Mexico. Common smut, caused by the fungus Ustilago maydis, is a common plant disease associated with developing ears of corn. While the appearance of the disease can by quite alarming, the disease usually affects only a few ears and is generally more of a curiosity than a real concern. In fact, in Mexico, after proper preparation, common smut is considered an edible delicacy and not a plant disease. Click here for more information on common smut. Contact: Natalie Goldberg
Cucumber Mosaic Virus
Cucumber Mosaic Virus - Are some of your vegetable plants deformed, twisted or elongated? Are the leaves mottled, wrinkled or curled? Are the plants stunted and not producing any fruit? If you answered yes to any of these questions, then your plants may be suffering from Cucumber Mosaic Virus (CMV). This spring we have had a significant number of plants submitted to the NMSU - Plant Diagnostic Clinic (NMSU-PDC) which have tested positive for CMV. This is a common virus, worldwide, and is present every year in New Mexico; but it usually appears later in the growing season and very sporadically. Already this year, we have had a number of greenhouse or hoop-house grown plants infected with the disease. Click here for more information. Contact: Natalie Goldberg
Freeze Damaged Plants
Freeze Damaged Plants - To save or not to save, that is the question! The freeze of February 2011 was significant indeed - many areas in New Mexico reported record or near record lows. Las Cruces recorded a low of -5 F and over two days when the temperature did not rise above freezing! Now that spring has arrived, we can start to assess the damage to plants from this event. Perhaps surprisingly, many plants have come out of the winter with no signs of any damage. Unfortunately for others, the story is not so bright. Some plants were killed. Others are struggling to survive. Plants that are still alive, but severely damaged, need to be assessed individually to determine the most appropriate fate. These damaged plants are predisposed to attack by pathogens and insects. In some cases, it may be best to remove these plants than to deal with disease and insect infestation later. If a decision is made to try and save these plants, damaged tissue should be removed in order to eliminate tissue that is attractive to pests. Click here for more on this story. To view videos on how to manage freeze damaged plants featuring the Dona Ana County Extension Agent, click here. Contact: Natalie Goldberg
Curly Top Virus
Curly Top Watch - It's that time of year again, Beet Curly Top Virus may soon be appearing in your gardens. Are your tomato plants curly and not producing fruit? Are your pepper plants stunted and yellow? How about your spinach, squash or beans? Are they deformed, stunted and/or yellow? If you answered yes to any of these questions, your plants might be infected with a disease called Beet Curly Top Virus (BCTV). BCTV is a common disease in many vegetable crops, including tomatoes, peppers, beans, pumpkins, squash, and spinach. It also infects many weeds, which serve as important alternate hosts allowing the virus to survive between growing seasons. The virus is spread from plant to plant by the beet leafhopper. The disease can start appearing in gardens shortly after planting and may continue to infect plants throughout the growing season. Although the lack of significant fall rain would generally indicate that the level of BCTV this year would be relatively low, we have already noticed a significant infection (over 50%) in a spinach planting in the Mesilla Valley. Click on the link above for a publication on this disease. Click here for more photos. Contact: Natalie Goldberg