- Author: Ben Faber
With all the rain last year, even extending into August and now with the rains since December there is a lot of natural ground cover growing, When it gets out of hand, we call it weedy. It might still serve the purpose of protecting the ground from erosion, but it can become an impenetrable mess and if allowed to go into summer, a major fire hazard. In the case of some young orchard, the malva and mustard is bigger than the trees themselves. Getting control of them before they get woody and go to seed is easier earlier than later. So it's time to do something about them if you haven't done so already.
A common practice on flat ground is to mow the middles and then weed whack/whip the tree row up to and around the tree trunk. In the case of trees that have their canopies down to the ground or near the ground or that have created a thick leaf mulch, there's not usually much weedy growth near the trunk. Then weed whacking around the canopy is not much of a problem. If on a slope like most avocados, it's a big, expensive, laborious, hot, sweaty, arduous process of weed whacking. Just waiting long enough for the leaf mulch to create a barrier to weed growth and for the canopies to grow out to rob the sun from the surface undergrowth.
In young trees without a large canopy, it can be a really difficult process of getting those weeds near the trunk. Care must be taken to avoid damage to the trunk. In a couple of recent examples, weed whacking got right up and on the trunks and significant damage was done to the trees. When a wound occurs in any tree, a process kicks in to generate tissue to cover the wound, much like what happens with humans and wound cuts. There's a scar left, but it heals over. If the wound is too large, many trees cant cover the woody tissue fast enough. The wood beneath the cambium ( the green tissue below the bark) is prone to fungal infection and eventually the fungus eats away at the interior of the tree. If the wound is large enough and girdles the tree, all the nutrients from the leaves feeding the roots is cut off. The photosynthate sugars that keep the roots functioning, and the roots stop doing what roots do. This is absolutely true is citrus and most other orchard tree crops. But not avocado.
When making a cross section of most trees, it's possible to see the growth rings – the growth increments that appear each year. The tree starts and stops growth each year and it's possible to clearly identified in what year there was more or less growth. In long lived trees like redwood, it's possible to identify years when certain events happened – the year of Lincoln's Gettysburg Address, for example. This growth habit is called ring porous.
In the case of avocado, it has a growth habit called diffuse porous. There is growth throughout the year and the rings are nor clearly delineated, if at all. It's because of this possible active growth occurring, that the avocado can often cover over damage that is quite extensive. After a fire, given time, mature avocado trees can summon up energy to recover to a great extent. It's not so true of young trees, however. Avocados still have a greater regenerative capacity than a lemon tree, and if the damage is to just one side of the tree, there's a very good chance of recovery.
But these young tree are severely impaired. They do have a chance of recovery, but the damage is extensive and the trunk is fully girdled. Only time will tell if they do recover. If the tree were only a year old, it would be a good idea to pull them and start over. But a number of these trees are three years old and have had a lot of investment in them besides their initial nursery cost – pruning, weeding, irrigation, fertilization, etc. It is heart breaking to see damage like this after so much attention has been paid to them.
And the best thing is to let the tree recover on its own. Use of pruning paint actually impairs tissue regeneration. The grower asked if a kaolin protectant like Surround might be used to provide some sun protection. Since that breathes, it might be a good idea. It might also be a good idea to apply some trunk wraps. These were taken off in order to prevent earwig and snail harbor which can cause significant damage to young trees. But they also provide protection from overly aggressive weed whackers. It is always a compromise when making these decisions.
- Author: Pershang Hosseini
- Author: Alison Colwell
- Author: Bradley Hanson
- Posted by: Gale Perez
The Orobanchaceae family comprises 270 holoparasitic species that cannot photosynthesize. Instead, they rely entirely on the host plant roots for nutrition, and can produce great numbers of minute, dust-like seeds that last for years in the soil. This family contains some of the most serious agricultural parasites in the genera of Phelipanche and Orobanche some of which are present in California. The different species can be distinguished by the degree of branching of their stems and presence/absence of bracteoles at the base of the flower Orobanche species have unbranched stems and no bracteoles, while Phelipanche species feature branched stems with bracteoles. In this paper, we discuss three economically significant broomrape species, and two that are not crop pests.
Phelipanche ramosa (Branched broomrape)
The natural distribution of branched broomrape (Table 1, Figure 2b) encompasses Europe, the Middle East, West Asia, and North Africa. It is established in southern Africa, Chile, and north America, having been reported in IL, TX, WA, OR, DE, WV, VA since early in the last century. Notable new infestations have been documented in Australia, resulting in several million dollars in annual expenses for quarantine and control efforts across 200,000 hectares. Further economic losses accrue from restrictions on the sale of produce or crop seed from the infested areas; these measures are aimed at preventing the spread of the parasite to other agricultural fields (Warren, 2006). Although reported occasionally in California in past decades, a new infestation of branched broomrape has been documented in California in recent years (Osipitan et al., 2021).
The host range of branched broomrape is exceptionally broad, encompassing various crops in the Solanaceae (tomato, eggplant, tobacco, pepper, and potato), Brassicaceae (rapeseed), Cannabaceae (hemp), Fabaceae (chickpea, clovers, groundnut, faba bean, lentil, pea), Apiaceae (carrot, celery, fennel, parsnip) and Asteraceae (lettuce, sunflower, and many ornamental species). Furthermore, branched broomrape can parasitize wild hosts within a range of families, including Chenopodiaceae, Amaranthaceae, Malvaceae, and Rosaceae. Although there have been reports of it affecting onions, it typically does not infest monocots.
There is evidence of lineages of this species having undergone both host specialization and host extension. For instance, one population initially parasitizing tomatoes was found to also parasitize tobacco and lettuce. In southwestern Germany, some farmers switched from cultivating tobacco to parsley, leading to an infestation of branched broomrape in the parsley crop (Kohlschmid et al., 2011). However, a population originating from tobacco failed to parasitize lettuce (Musselman & Parker, 1982), suggesting the host shift requires some selective adjustments in order to succeed.
Economic Importance: Yield losses in tomato and tobacco are commonly reported to be 30–50% (Parker, 2013). Branched broomrape was found to reduce tomato shoot dry weight by 60-70%, while also causing a concurrent 50% decrease in chlorophyll content and photosynthesis levels (Mauromicale et al., 2008) in pot experiments.
Phelipanche aegyptiaca (Egyptian broomrape)
Branched and Egyptian broomrape (Table 1, Figure 2a) are closely related and easily confused for one another. Egyptian broomrape is a more robust, taller plant than a typical branched broomrape plant but the most easily noted difference is the larger size of the flowers at 20–35 mm long (branched broomrape typically no more than 20 mm). The distribution of Egyptian broomrape overlaps with branched broomrape in South Europe, the Mediterranean, and North Africa but extends much further eastwards into South Asia and China.
Egyptian broomrape can attack most of the same crops affected by branched broomrape. It differs in occurring on a wider range of Brassicaceae, especially various mustard species in India. It is also a more important pest on Cucurbitaceae compared to branched broomrape.
Economic Importance: The effects of Egyptian broomrape on the host are the same as branched broomrape, and damage can be similarly severe.
Orobanche minor (small broomrape)
Small broomrape (Table 1, Figure 2c) is typically a one (or few) stalked, unbranched plant up to 70 cm tall and occasionally 1 m. It is very widely distributed, being native throughout most of Europe, Western Asia and Northern Africa, as far south as Ethiopia and Somalia, while it has also been sporadically introduced to Japan, New Zealand, Australia and several countries in North and South America. This species is a federally listed noxious weed in the United States that has infested red clover fields in Washington and Oregon (Mallory-Smith & Colquhoun, 2012; Osterbauer & Rehms, 2002 ).
The host range for small broomrape is very wide, particularly in Fabaceae (clover, alfalfa, vetch). Small broomrape can also parasitize Asteraceae (lettuce, safflower) and Apiaceae (carrot, celery), Solanaceae, and other families.
Economic Importance: The greatest economic damage is to clover, reported in several countries in Europe. This problem has led to the abandonment of the clover seed industry in some of those countries including the UK.
Orobanche hederae (ivy broomrape)
While the majority of Orobanche species exhibit a broad host range for parasitism, some, such as ivy broomrape (Table 1, Figure 2d), exhibit narrow preferences. In this case, the parisite exclusively attacks species within the Hedera genus, commonly known as ivy. Ivy broomrape is a short-lived monocarpic perennial, reaching heights of up to 60 cm. Its distribution area spans across Western and Southern Europe, North Africa, and Asia Minor. It is a close relative of Orobanche minor, and arguably derived from it.
Economic Importance: None known.
Aphyllon Cooperi or Orobanche Cooperi (desert broomrape)
Desert broomrape (Table 1, Figure 2e) is a biennial broomrape that is native to the desert southwest of the US and Mexico. It parasitizes shrubs of Ambrosia and Encelia (Asteraceae). It was segregated from Orobanche based on chromosome number and 5 calyx lobes instead of 4.
Economic Importance: None known. It has been reported occasionally in tomato fields, but does not appear to persist under cultivation of the crop. It has been grown in potted tomatoes by the second author, but it is slow to reach the flowering stage and the phenology unfolds slowly, so the plant is unlikely to set seed during a tomato crop produciton cycle.
References
Kohlschmid E, Mu¨ller-Sto¨ver D, Sauerborn J. (2011). Ausbreitung des parasitischen Unkrauts Phelipanche ramosa in der deutschen Landwirtschaft. Gesunde Pflanzen, 63:69–74.
Mallory-Smith, C., & Colquhoun, J. (2012). Small broomrape (Orobanche minor) in Oregon and the 3 Rs: regulation, research, and reality. Weed science, 60(2), 277-282.
Mauromicale G, Lo Monaco A, Longo AMG. (2008). Effect of branched broomrape (Orobanche ramosa) infection on the growth and photosynthesis of tomato. Weed Science, 56: 574–581
Musselman LJ, Parker C. (1982). Preliminary host ranges of some strains of economically important broomrapes (Orobanche). Economic Botany, 36:270–273.
Osipitan O, Hanson B, Goldwasser Y, Fatino M, Mesgaran M. (2021). The potential threat of branched broomrape for California processing tomato: A review. Calif Agriculture, 75(2):64-73. https://doi.org/10.3733/ca.2021a0012.
Osterbauer, N. K., & Rehms, L. (2002). Detecting single seeds of small broomrape (Orobanche minor) with a polymerase chain reaction. Plant Health Progress, 3(1), 1.
Parker, C. (2013). The parasitic weeds of the Orobanchaceae. In Parasitic Orobanchaceae: parasitic mechanisms and control strategies (pp. 313-344). Berlin, Heidelberg: Springer Berlin Heidelberg.
Warren, P. (2006). The branched broomrape eradication program in Australia. In: Preston C, Watts JH, Crossman ND (eds) 15th Australian Weeds Conference, Adelaide, September 2006, pp 610–613.
- Author: Mackenzie Patton
- Posted by: Gale Perez
The Invasive Pest Spotlight focuses on relevant or emerging invasive species in California. In this issue we are covering brooms, a group of invasive shrubs.
Brooms are upright shrubs in the legume family that typically produce small, yellow, pea-shaped flowers. Shrubs range from 3 to 10 feet tall. They produce flowers from mid spring to summer and produce seed pods in late summer. All brooms are prolific seed producers, with a single shrub producing as many as 2,000 to 3,500 pods containing up to 20,000 seeds.
While brooms are attractive plants, they grow in dense stands that outcompete many native plants. These dense stands are highly flammable and increase the risk of wildfires. The most common species found in California are Scotch broom, French broom, Spanish broom, and Portuguese broom. Scotch broom is often found on interior mountains and on lower slopes in Northern California and is very prevalent in the Sierra Nevada foothills. Without management, these plants can survive for about 12 to 17 years, producing thousands of seeds.
Actions You Can Take
First, avoid planting any broom species. While most retailers do not sell the most common invasive brooms, many do sell hybrids that could become highly invasive in the natural landscape. There are similar-looking alternatives to brooms, such as forsythia and golden currant. Contact your local UC Master Gardeners or visit PlantRight.org for a list of other alternatives.
If you have brooms on your property and want to remove them, there are many different nonchemical and chemical methods that are effective in controlling these plants. These options are extensively detailed in the UC IPM publication Pest Notes: Brooms.
Original source: UC IPM's Home & Garden Pest Newsletter Summer 2023 issue
- Author: Mackenzie Patton
The Invasive Pest Spotlight focuses on relevant or emerging invasive species in California. In this issue we are covering brooms, a group of invasive shrubs.
Invasive Broom facts
Brooms are upright shrubs in the legume family that typically produce small, yellow, pea-shaped flowers. Shrubs range from 3 to 10 feet tall. They produce flowers from mid spring to summer and produce seed pods in late summer. All brooms are prolific seed producers, with a single shrub producing as many as 2,000 to 3,500 pods containing up to 20,000 seeds.
While brooms are attractive plants, they grow in dense stands that outcompete many native plants. These dense stands are highly flammable and increase the risk of wildfires. The most common species found in California are Scotch broom, French broom, Spanish broom, and Portuguese broom. Scotch broom is often found on interior mountains and on lower slopes in Northern California and is very prevalent in the Sierra Nevada foothills. Without management, these plants can survive for about 12 to 17 years, producing thousands of seeds.
Actions you Can Take
First, avoid planting any broom species. While most retailers do not sell the most common invasive brooms, many do sell hybrids that could become highly invasive in the natural landscape. There are similar-looking alternatives to brooms, such as forsythia and golden currant. Contact your local UC Master Gardeners or visit PlantRight.org for a list of other alternatives.
If you have brooms on your property and want to remove them, there are many different nonchemical and chemical methods that are effective in controlling these plants. These options are extensively detailed in the UC IPM publication Pest Notes: Brooms.
[Originally featured in the Summer 2023 issue of UC IPM's Home & Garden Pest Newsletter]
[Originally featured in the Winter 2022 Issue of UC IPM's Green Bulletin Newsletter]
Weeds can be a problem in any landscaped areas including around trees, shrubs, flower beds, or lawns and turf. As we move from cool weather to warmer temperatures, you will see winter weeds grow and become a problem in established landscape plantings. Effective control of weeds include hand-weeding, hoeing, mulching, and herbicide applications. Good management depends on early attention to where weeds are establishing and adjusting the conditions that allow them to thrive.
Managing weeds in landscape plantings
Each type of planting bed will have specific techniques that work best. In general, dense plantings will shade out most weeds. Regardless of the type of landscape bed, it's always best to control perennial weeds before planting. Herbicides are effective in many types of landscape plantings. They are most effective when integrated with cultural practices. Many of the herbicide active ingredients available for weed control in landscape plantings are only for use by pest management professionals.
Tree and shrub beds
Landscaped areas made up of trees and woody shrubs don't need as much preplant weed control as other types of beds. Control perennial weeds after planting using methods like mulching, hand pulling, and herbicide treatments. Suppress weed growth by laying down landscape fabric, then adding an inch of mulch on top to thoroughly cover the fabric. If needed, use a preemergence herbicide. Supplement with spot treatments of postemergence herbicides and hand-weeding.
Ground cover beds
Since ground cover is expected to fill the entire bed, landscape fabric is not suitable for weed suppression. Perennial weeds should be controlled before planting. If perennial grasses are encroaching, they can be controlled with selective herbicides like fluazifop, clethodim, or sethoxydim. Spot applications of glyphosate or glufosinate can be used on perennial weeds. Mulch the bed to control annual weeds until the ground cover fills the area. Some hand weeding might be needed.
Annual flower beds
As with other landscaped areas, a dense planting will shade out weeds. Annual weeds can be managed with mulches, frequent cultivation, and hand-weeding. Periodic cultivation (every 3 to 4 weeks) will suppress many weeds. Since nonselective herbicides can't be used after planting annual beds, it's easier to manage perennial weeds beforehand. If cultural methods aren't working to control perennial grasses, you can use grass-selective herbicides with clethodim or fluazifop. Check the product label to be sure that it won't harm the annual flowers in the bed.
Herbaceous perennial beds
Manage weeds in herbaceous perennial beds as you would an annual flower bed. Be sure to get rid of perennial weeds before planting since the bed will be growing for more than one season. Use landscape fabric where possible along with mulches. You might need to supplement with hand-pulling followed by preemergence herbicides. Be aware that fewer perennial plants are included as sites on herbicide labels.
Mixed plantings
A planting bed of a mix of woody and herbaceous plants is a more complex situation. Different areas of the bed might need different treatments. Post-plant herbicide choices are limited so site preparation is critical in this type of bed. Plant woody species first and control the perennial weeds. After the first two growing seasons, add the herbaceous plants. Shade the soil with close planting. Group plants within the bed based on their weed management needs.
Cool weather weeds in landscapes
Some of the most troublesome weeds in planting beds during late winter and early spring are common groundsel, oxalis, mallows, and nutsedges.
Common groundsel
Common groundsel is most prolific in cool weather, germinating from seeds this time of year. This weed produces many seeds and can rapidly infest landscape beds. It is best controlled before it flowers. Mulch is highly effective at controlling common groundsel. Young plants can be hoed out. Diquat or glyphosate-based herbicides will control common groundsel in landscape beds.
Mallows
Mallows are annual weeds that begin growing with the first rains so you may already be seeing these sprouting up in landscape beds. This plant develops a long taproot so it should be pulled when it has four or fewer true leaves. At least three inches of mulch is needed to suppress mallow. Young mallow plants might be managed with 2,4-D products, but this herbicide will injure broadleaf plants growing nearby.
Nutsedges
Purple and yellow nutsedge are perennial plants that sprout in spring from tubers. Remove these weeds as soon as possible to prevent tuber production. Tubers (sometimes referred to as “nuts” or “nutlets”) are key to nutsedge survival. Once established, nutsedge plants are difficult to control. They don't grow well in shade so dense plantings of ground cover or shrubs will suppress nutsedges. Few herbicides are effective at controlling nutsedge.
Oxalis (creeping woodsorrel and Bermuda buttercup)
While Oxalis (creeping woodsorrel) can bloom almost any time during the year, spring is a time of heavy flowering and seed formation. Buttercup oxalis sprouts in fall and is a major weed in ornamental plantings. Hand pulling can control these weeds but be aware that mowing can spread creeping woodsorrel. Landscape fabric with two to three inches of an organic mulch on top can control oxalis. There are no selective postemergence herbicides for creeping woodsorrel in ornamental plantings.
Herbicide injury
Desired plants could be injured when herbicides are used in established landscape beds. Herbicide damage symptoms vary depending on the herbicide and the plant. Symptoms can include yellowing, bleaching, distorted growth, and death of leaves. Avoid herbicide injury by following the label about the site, plant, and application rate. Granular formulations are less likely to damage plants than sprays. When using a nonselective liquid herbicide, apply on a calm day using low pressure and large droplets. Use a shielded sprayer to avoid contact with nontarget plants. If plants are injured from soil-applied herbicides, the damage is often temporary but can cause growth inhibition. Adding organic amendments and keeping the soil moist will help the herbicides to break down faster.
For more details and for information about weed management before planting a landscape bed, see Pest Notes: Weed Management in Landscapes.
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