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from seed to harvest weed

Online Horticulture of Cannabis Courses

This summer (SS1: May 31 – July 1, 2022 & SS2: July 11 – August 12, 2022), UConn is offering two Horticulture of Cannabis courses (introductory and advanced) in convenient online formats. The two 3-credit courses can be completed 100% online from anywhere in the world and are designed to provide intensive overviews of the horticultural techniques used to grow and manage this medically important and high value crop. Both of UConn’s Cannabis Horticulture courses are delivered via an interactive and online platform, enabling you to engage with students, faculty and content within an asynchronous environment. Asynchronous means that you can sign on anytime of the day to complete assignments or participate in discussions.

Cannabis is one of today’s hottest and most lucrative crops. There is increasing interest in the U.S. about growing Cannabis as a recreational crop, and also medical usefulness of cannabinoids such as cannabidiol (CBD).

Both courses are taught by Matthew DeBacco and Gerald Berkowitz, resident experts within UConn’s College of Agriculture, Health and Natural Resources.

Concerning costs for each 3-credit Cannabis Horticulture course:

  • Many visiting (non-degree) students will pay $2,051 for 1 course and $4,037 for 2.
  • Most current UConn students will pay $2,031 for 1 course and $4,017 for 2.

Note: There are multiple exceptions and special cases concerning course costs, visit UConn’s Summer Sessions Dates & Fees Page to learn more.

Horticulture of Cannabis Summer Courses

Introduction to the Horticulture of Cannabis: Seed to Harvest

SPSS 2130 Horticulture of Cannabis: Seed to Harvest – This 100% online course focuses on growing cycles of Cannabis from both macro and microscopic scales. Students will develop an understanding of some of the common challenges with Cannabis production and how to best identify and correct these issues. Lectures focus on horticultural management of a Cannabis crop grown in the field and in controlled environment.

In this course, students focus on the fundamentals of the production cycle of Cannabis including horticultural management, identification of crop issues, elite feminized seed production, seed propagation, vegetative propagation, pruning, training, optimization of cannabinoid content, and post-harvest handling. And further, the course will overview business operations related to Cannabis world-wide and in Connecticut, explore lab testing procedures, cannabidiol extraction technologies, the Connecticut medical marijuana program, and government regulation of the industry. Taught with SAPL 130.

Course material will be presented at the introductory level; the class is designed for students with diverse academic backgrounds; there are no prerequisites. There is no laboratory component to the course. Cannabis plants will be grown for class demonstrations related to specific horticultural techniques.

Prerequisites: None

Advanced Cannabis Horticulture: Production & Industry

SPSS 3995 Special Problems: ‘Advanced Cannabis Horticulture: Production and Industry’ – This 100% online course focuses on growing cycles of Cannabis from both macro and microscopic scales. Students will develop an understanding of some of the common challenges with Cannabis production and how to best identify and correct these issues. Lectures focus on horticultural management of a Cannabis crop grown in the field and in controlled environment.

Students will develop a full understanding of the production methods of cannabis in addition to postproduction methods. Aspects of the industry will also be included to provide information about extraction, end products, jobs and current research within the cannabis industry. The organization of this course allows students to be able to choose their own progression through the course to allow for individual paths that will provide advanced level details. Students will be able to select starting plants from clones or seeds and if they plan on growing indoors or outdoors. Each student’s directed path through the course allows for a deeper understanding of the topics which are of greatest interest to the students that are connected with scientific research supported information. Job opportunities related to growing as well as other careers involved with the industry will be provided.

The class is designed for students with diverse academic backgrounds; there are no prerequisites. There is no laboratory component to the course. Cannabis plants will be grown for class demonstrations related to specific horticultural techniques.

Opportunities and challenges for harvest weed seed control in global cropping systems

The opportunity to target weed seeds during grain harvest was established many decades ago following the introduction of mechanical harvesting and the recognition of high weed-seed retention levels at crop maturity; however, this opportunity remained largely neglected until more recently. The introduction and adoption of harvest weed seed control (HWSC) systems in Australia has been in response to widespread occurrence of herbicide-resistant weed populations. With diminishing herbicide resources and the need to maintain highly productive reduced tillage and stubble-retention practices, growers began to develop systems that targeted weed seeds during crop harvest. Research and development efforts over the past two decades have established the efficacy of HWSC systems in Australian cropping systems, where widespread adoption is now occurring. With similarly dramatic herbicide resistance issues now present across many of the world’s cropping regions, it is timely for HWSC systems to be considered for inclusion in weed-management programs in these areas. This review describes HWSC systems and establishing the potential for this approach to weed control in several cropping regions. As observed in Australia, the inclusion of HWSC systems can reduce weed populations substantially reducing the potential for weed adaptation and resistance evolution. © 2017 Society of Chemical Industry.

Keywords: HWSC; Harrington Seed Destructor; bale direct system; chaff cart; chaff lining; chaff tramlining; herbicide resistance; iHSD; narrow-windrow burning; weed-seed retention.

Crop weeds: weed management at harvest

Please note: This content may be out of date and is currently under review.

This management strategy provides an opportunity to control weed seed set in the pasture and during harvest. It physically removes viable seed from the paddock by collecting weed seed and grazing crop residues.

Baling crop residue directly from the header.jpg

Seeds of grasses like barley grass are not highly palatable. These grasses need to be grazed before seed heads are produced.jpg

Modifications to the header to generate a narrow chaff trail concentrating weed seeds and allowing a hot burn.jpg


Weed seed removal can be achieved in two ways:

  • Harvesting provides an excellent opportunity to remove weed seeds from the system and prevent them from being spread across the paddock or farm. Collecting seed at harvest has the potential to be a useful component of an integrated weed management program.
  • Grazing weed contaminated crop residue can be a cost-effective way of controlling weed growth. Animal digestion of weed seeds prevents a large proportion of seeds from entering the seedbank.

Weed seed collection at harvest will not increase grain yield, as the weeds have already caused damage to the crop. The tactic can only prevent increases to the seedbank, although it may give a subsequent yield advantage to the next season’s crop through reduced weed numbers during the season.

Management of weed seed removal at harvest

Factors affecting weed seed removal

The weed species has a major influence on the proportion of weed seed removed from the paddock when collected at harvest. For example, annual ryegrass is much more available to collect than wild oats, which tend to shed seed before harvest. Successful collection and control depends on the weed:

  • Maturing at the same time, or later than, the crop being harvested.
  • Having seeds at a similar or greater height compared with the crop being harvested — this may be overcome by setting the header at a height so weed seeds are captured.
  • Having seeds that do not shed or shatter before or during harvest.
  • Having seeds that can be threshed and are of a size that end up in the chaff component of the harvested crop.
  • Timing of harvest will affect the amount of seed removed from the paddock when residue is collected. As harvest is delayed, a greater proportion of the weeds presented will shatter or lodge, reducing the total proportion of seed able to be collected.

Disposal of chaff and seed

A strategy to dispose of chaff dumps or large quantities of baled straw must be implemented. These two products will contain the collected seed and therefore need to be managed appropriately. Chaff dumps are usually burned or fed to livestock, and both options require careful management.

Methods of weed seed collection at harvest

Narrow header trail

Facilitating narrow header trails (also known as trash windrows) is the cheapest, simplest form of collecting residue. It is done by disconnecting the straw spreaders on the header and allowing the straw, chaff and weed seeds to fall in a narrow trail behind the header. Adding a simple chute forces the residue into an even narrower, more discrete row.

The trail can then be burned during autumn. This has become common practice in many districts when harvesting canola. The high fuel load in the row results in a hot burn and a good weed seed kill. However, any unburned seeds will produce seedlings that will need to be controlled using an alternative tactic.

In a controlled traffic cropping system, straw can be spread while chaff and weed seed are deflected onto the wheel track where they are less likely to grow. During the subsequent growing season spray nozzles can be fitted to another implement to apply a non-selective herbicide to the wheel tracks, killing any germinated weeds. This system fits well where there is a preference for avoiding burning.

Chaff cart

In a chaff cart system the chaff and weed seeds are collected and thrown into a trailing cart. When the cart is full the gate is tripped and the cart self-empties to create a chaff dump.

Harrington seed destructor

Ray Harrington has invented the Harrington Seed Destructor (HSD). Ray first observed a cage mill rendering coal at a Collie coal mine and he decided that this was the type of mill he needed to destroy weed seeds. Testing of the HSD shows that it has the ability to destroy 90-95% of the weed seeds in the chaff it processes. The HSD entered commercial production in 2012 and is now available incorporated into a header (Integrated Harrington Seed Destructor, iHSD)

Other options for weed seed collection at harvest

Baling systems

Baling the chaff is an alternative to grazing. Because the material is already chopped, chaff bales are more attractive to dairy farmers than the conventional straw bales. As proximity to market and price can be limiting factors, this option appeals to those growers who have access to a stock-feed market such as a dairy, beef feedlot or stock-feed mill.

Grazing crop residues

Grazing weed-contaminated crop residue can be a cost-effective way to control weed growth. Animal digestion of weed seeds prevents a large proportion from entering the seedbank.

Benefits from grazing crop residues for weed management

  • Grazing reduces the number of weed seeds added to the seedbank.
  • Grazing can be used to dispose of, and gain value from, weed seed contaminated fodder.
  • Weed seeds can provide a significant proportion of the nutritional value when stock graze crop residue (note that the feed value of the residue will be variable).
  • Post-harvest grazing may reduce crop establishment problems through reduction in stubble burdens.

Other factors to consider

  • Seed burial through trampling may enhance weed germination pre-sowing. Using a knockdown herbicide and delaying sowing can then capitalise on this.
  • Seed of desirable plants (pasture species) may be distributed in faeces.
  • Grazing livestock can distrubute weed seeds across a paddock.
  • The impact of grazing on weed numbers in the seedbank is dependent on the biological features of the weed. Grazing is successful in reducing weed seed numbers in palatable weeds and where the seeds can be easily eaten and digested. However, seed palatability varies from weed to weed. The presence of awns, thorns or biochemical traits makes some weeds less attractive to grazing animals than others.
  • Seed location: Stock must be able to access seed to ingest it. Seed still in the head, or in chaff dumps or feed troughs, is easier to access than seed lying on the soil surface.
  • Seed size: When shed from the seed head, small seeds are more difficult for animals to graze. Small seeds are also more likely to survive ingestion and digestion.
  • Hard seeds: A high proportion of hard seeds will remain viable after digestion. The digestive process can also break seed dormancy, encouraging the germination of seeds shed in faecal matter.
  • Livestock trampling tends to bury weed seed, which can decrease the efficiency of burning as a means of killing seeds. Depending on the weed species, burial may also increase germination rates.
  • Grazing may cause an increased risk of soil, water and wind erosion, increased soil compaction and potential toxicity issues for sheep, for example, lupinosis and annual ryegrass toxicity.

Grazing – actively managing weeds in pastures

In crop based rotations, a 2-3 year pasture phase may significantly reduce weed seedbanks to manageable levels before returning to a cropping phase. Pasture weed management requires maintaining desirable legume and grass species while keeping weed numbers under control.

Grazing, in association with other tactics, may be used to help reduce weed numbers. Grazing can be coupled with hay and silage making, mowing and pasture spray-topping for increased weed control. Well managed grazing will increase legume composition and improve feed quality.

Issues to consider when controlling weeds in pasture

Grazing pressure

Even though your newly established pasture may look lush and inviting, avoid the temptation of grazing too soon.

High grazing pressure is necessary to ensure weed control. Insufficient grazing pressure (particularly in spring when the seed heads of some grasses may be less palatable than legume species) will not result in weed control. However, high grazing pressure can increase the proportion of broadleaf weeds like capeweed and erodium. Stock avoid these weeds because it is difficult for them to graze species with a flat rosette. Using a herbicide to cause these species to curl their leaves will give stock better access to them, but grazing pressure must be high to ensure that stock eat these broadleaf weeds.

Timing of grazing is critical

High grazing pressure in autumn will physically remove small weed plants, and short periods of intense grazing are generally recommended to minimise damage to non-weed species. However, optimal grazing management depends of the ecology of the pasture species and weeds in question. For example, silver grass species are best managed by light grazing pressure in autumn, and light grazing pressure will also avoid the development of bare areas where weeds may establish at a later date.

High grazing pressure in spring will reduce weed seed production, but will also reduce seed production by desirable pasture species. Sheep and cattle will preferentially graze the small heads of annual ryegrass. However, sharp awned seeds from grasses like brome grass, barley grass and silver grass are not palatable to stock. So intensive spring grazing to control these species should commence prior to emergence of the seed head.

Grazing can be used in conjunction with herbicides (spray-grazing) to effectively manage weeds

Spray-grazing refers to the use of sublethal rates of selective herbicides (often phenoxy-based) to increase the palatability of broadleaf weeds for preferential grazing. It is usually undertaken in autumn or early winter and is especially beneficial for the control of erodium, capeweed, Paterson’s curse and wild radish. The use of phenoxy-based herbicides causes the flat weeds to curl up and thus become more accessible to livestock.

High stocking rates (up to four times the normal rate for the area) are required for spray-grazing to work effectively. Weeds that are not killed by spraying alone will recover in 2-3 weeks and exhibit normal growth if they are not grazed heavily after spraying.

Burial of seeds

Livestock movement will bury some weed seeds. In some cases this will enhance germination and subsequent weed control. However, this may alternatively allow the seeds to escape other weed control techniques like burning. Consider what weed species are in the field, and how burial will affect subsequent weed control.

Manage grazing to avoid the risk of livestock transporting weed seeds

Practicing good farm hygiene techniques will assist in minimising weed seed transfer.

  • Move stock to holding areas after they have grazed weedy fields.
  • Keep new stock in holding areas for at least five days to empty any seeds in the gut before allowing them to graze other fields on the farm.
  • Keep stock in containment areas when hand-feeding with imported feed.
  • Alter shearing schedules to ensure that fleece length is short when grasses are shedding seed (this will also reduce vegetable fault in fleeces).

Timeline for the implementation of tactics for management of annual grass weeds in pastures. Note that for Western Australian wheatbelt pastures, a dry matter maintenance target is >800kg of plant material per hectare.