study set 5

What is a pathogen, and what are the three major classes of plant pathogens?

A pathogen is a disease-causing living organism. Fungi, bacteria, viruses

What are some features that would make a plant a very effective weed in agricultural systems?

"good" weeds establish themselves quickly: - they do well in regularly disturbed environments - they grow quickly - they are often annuals - they are very competitive (with other plants) for nutrients and water "good" weeds also reproduce very well: - they can self-pollinate or propagate vegetatively - they produce a LOT of seeds - they have effective seed dispersal mechanisms - seeds lay dormant, so they don't germinate all at once (making them vulnerable to one stressful event killing all of them)

What are some strategies that we can take to protect and save genetic diversity in agricultural crops and livestock?

- Maintain centers of diversity (which are often found where crops were originally domesticated). Landraces and wild relatives are often found in these spots. - Maintain gene banks, which store seeds, plant material, and reproductive cells (eggs and sperm) of animals. - Actively use genetic resources that are preserved in gene banks and that have been collected by plant breeding. - Have smaller-scale producers and interested hobbyists preserve heritage or heirloom varieties in various grassroots efforts.

What are some key practices that are part of integrated pest management?

- avoiding conditions that favor pests/diseases - using cultural methods to control pests - monitoring regularly for pests - relying on natural enemies to control pests - use pesticides as a last resort (and try to use the most specific pesticide possible).

What are some examples of cultural pest and disease management techniques?

- crop rotation - sanitation of planting materials - barriers; e.g. fences, rowcovers. - trap crops - using deterrents to pests - physical removal of pests

The 'plant disease triangle' concept is used to describe how much potential exists for a major disease problem. Explain this idea. Using this concept, describe three basic strategies to reduce the likelihood of a plant disease outbreak.

1) the pathogen, 2) the environment, 3) the plant. For diseases to take off, you need to have the pathogen present, to have environmental conditions that are conducive to the pathogen, and lastly, you need to have a susceptible host plant. To prevent diseases, you can try to reduce all of these - eliminate the pathogen by using good sanitation, make the environment unfavorable for pathogens (minimizing humidity, is one way to do this), and lastly, remove susceptible hosts-by using crop rotation and selecting resistant varieties of crop plants.

What are two strategies for reducing the weed seed bank?

1. Cut down weedy plants before they go to seed. 2. Try to reduce introducing weed seeds in compost and manures being imported into farm.

Name three differences between conventional and organic dairy farming

1. Organic dairy cows must be on pasture at least 120 days per year 2. Organic dairy cows must hjave 24 hour/7 day a week access to the outdoors 3. Organic dairy farms are forbidden to use antibiotics 4. Organic dairy farmers must feed their cows all certified organic feeds

What is a disorder (as compared with a disease)?

A disorder is caused by non-living (abiotic) or environmental stress.

Why is genetic diversity essential for making sure that we can sustain agriculture into the future?

A diverse population is resilient and capable of adapting to a change in the environment. In the case of agriculture, this could also be a change in the production system. Maintaining genetic diversity means that we will have access to traits that we may need in "varieties of the future", such as disease and pest resistance, adaptation to harsh conditions or low inputs, etc.

what is a weed?

A weed is a plant out of place; whose undesirable qualities outweigh its good points.

Define Aquaculture

Aquaculture could be defined as the farming of marine and freshwater plants and animals for human consumption (food), recreation, baitfish, or restocking. Aquaculture is a form of agriculture using water as the medium, instead of soil.

Define aquaponics, and describe basic functioning of an aquaponics system.

Aquaponics is the combination of aquaculture (raising aquatic animals) with hydroponics (raising plants in nutrient-enriched water). We saw several small-scale examples of aquaponics systems; the idea with all of these is that with fish feed as the primary input, fish waste in the water is converted into plant-available forms of nutrients, and plants harvest those nutrients from the water, simultaneously cleansing the water. The goal is to produce two types of food (typically fish and plants) at the same time.

What is Bt and how does it work?

Bt refers to the soil bacterium Bacillus thuringiensis. Bt is a biological insecticide that is used by organic growers. Bt produces a toxin that specifically targets some caterpillars of the order Lepidoptera. Bt colonizes leaf surfaces with spores and crystal structures which dissolve in the caterpillar's midgut causing it to die.

List several cultural or mechanical approaches to managing or controlling weeds.

Crop rotation, cover cropping, altering dates that you plant a crop, altering crop plant densities, altering row orientation, using fallow periods (where a field is left bare, without a crop) are all examples of cultural weed management. Mechanical approaches to managing weeds include tillage, cultivation, hoeing, and hand pulling weeds.

What are some problems with certain types of aquaculture systems? Give an example or explain each problem you describe.

Environmental degradation - shrimp ponds constructed at the interface between ocean and mangrove swamps destroys critical habitat for many species. Crowded fish cages - when there are too many fish in too many closely spaced fish cages, water does not flow through to refresh, leading to contaminated water (nitrates and other waste products, etc.) where the fish are growing. Antibiotic use - in crowded conditions, disease is more likely. Where it is allowed, antibiotics are sometimes used preventatively.

In class, we discussed several microbial, mineral and botanical pesticides that organic growers can use. Give two examples of these pesticides and their mode of action (or how they work).

Ex) Spinosad - nerve and stomach poison to many insects Ex) Coppers - disrupts cellular proteins in fungi, bacteria Ex) Pyrethrum - harms insect nervous systems Ex) Bacillus thuringiensis (Bt) - toxin dissolves caterpillar midgut lining

What are some of the reasons that we have relatively narrow genetic diversity represented in the crops and livestock that are grown commercially today? Can you give any examples where we have very little genetic diversity within mainstream agriculture?

Examples of limited diversity that we mentioned in class included: corn, banana and wheat... though the same is true for many other food crops and livestock species. Reasons we're in this situation include: - Consolidation in the plant breeding and seed supplying industries - Uniform agricultural production systems (therefore needing less genetic variation in crops). - Large scale distribution of crops (favors uniformity of crops)

What are some of the ways that genetic engineering has been used in commercial crops?

Genetic modification is a way to add traits that aren't available in that plant already. The most common traits are herbicide tolerance, insect resistance, and virus resistance. The very first GE crop was the Flavr Savr tomato, which ripened more slowly than normal tomatoes. And 'golden rice' contains genes that make vitamin A, which is not normally found in rice. Other areas under research include using crop plants to produce pharmaceutical and industrial compounds. Round-up resistant GE corn and soybeans are currently being produced in large quantities in the US, Brazil and parts of Asia.

We discussed one example of a GE fruit crop, the transgenic 'Rainbow' papaya, which is resistant to papaya ringspot virus. It was released to growers in Hawaii in 1998. What are some of the effects that it has had?

Growers adopted the transgenic papaya, and production was so good that supply exceeded demand and prices paid to the growers fell Non-transgenic papaya can now be grown again in HI (because the abundance of transgenic papaya reduces the amount of trees that could act as a source of infection for the virus). Some organic and conventional non-transgenic papaya growers are concerned with the drift of pollen from the GM papaya onto their crops. Other viruses still infect the papaya, it is not immune to other diseases.

What is meant by the term "heirloom vegetable seed"

Heirloom seeds are seeds which have passed down through generations of farmers which are open pollinated and desirable for their taste, flavor, and adaptation to their local growing conditions. There has been a recent spark in interest in the utilization and preservation of these varieties. For many years they were largely ignored since they often do not lend themselves to uniform industrial style production.

What is the difference between a hybrid crop and a genetically modified and an open pollinated crop?

Hybrid crops are developed by crossing two varieties of a crop plant (e.g. one corn variety with another corn variety). generally more uniform and have higher yields than inbred or 'open-pollinated' varieties. Hybrid seeds are labeled as F1 in seed catalogs. Hybrid seeds cannot be saved and re-planted the following year as they will not produce "true to seed" in the following generation (F2). Like GE crops, hybrid seeds, therefore, must be purchased each year. GM or GE crops refer to plants that contain a gene from another organism. That gene could be from a plant, or a bacterium (like with Bt corn, which contains the gene from the bacterium Bacillus thuringiensis). Hybrid crops are often grown on organic farms; GM crops are not permitted. Open pollinated seeds are traditional varieties which can be saved by farmers/gardeners season and after season and replanted. When replanted, the seeds will produce "true to seed"

We spoke earlier in the class about features that would make a good cover crop. Would weeds make good cover crops? Describe.

Many features of effective cover crops (fast growth, competitive, annuals, produce a lot of seeds, etc.) are shared with effective weed species. Typically, with a cover crop, we want all seeds to germinate when we plant them, so we don't want dormancy. As long as we take precautions and prevent weeds from producing seeds, they would make a good cover crop. However, in most cases, they set seeds very quickly, making this difficult.

What are some examples of things that can cause symptoms of a disorder?

Moisture extremes - drought, flooding, over-watering Temperature extremes - heat, sun-scald, freezing Physical injury - human, animal, weather (hail) Chemical - fertilizer, salt, pesticides, nutrient imbalances

What kinds of pesticides can be used on organic crops? Are any of them synthetic?

Pesticides that appear on The National List in the organic standards can be used. A few synthetic pesticides are permitted, but most are natural products derived from minerals, microbes or plants.

What is the primary goal of a long term weed management plan?

Reduction of the weed seed bank. The weed seed bank is the sum of all of the weed seed lying dormant in the soils of an agricultural field. Weed seeds which have germinated and are currently growing comprise what is known as weed pressure.

What is the difference between symptoms and signs of a disease? Give at least five examples of types of symptoms, and give one example of sign.

Symptoms = physical expression of disease, i.e. abnormal appearance Examples include - chlorosis, necrosis, blights, rots, spots, holes, leaf distortion, and more. Signs = physical evidence of the pathogen that is causing the disease Examples include - the mycelia of fungi, bacterial oozes, etc.

What is the LD50 of a chemical?

The LD50 measures the ACUTE toxicity of a chemical. It is the amount (mg per kg of body weight) of the material required to kill 50% of the test subjects. A lower LD50 means a MORE toxic material.

What is the difference between the pesticide Bt and a transgenic Bt crop?

The pesticide with the active ingredient Bt is sprayed on crops. It is considered a natural biological insecticide, so it is permitted for organic growers to use, and many growers do use it. Transgenic Bt crops are crops that contain the gene from the Bacillus thuringiensis bacterium and therefore produce the Bt toxin in each plant cell. It is considered a "biopesticidal plant" because it produces the Bt pesticide all on its own. Because Genetic Engineering is a prohibited technology for organic growers (it is synthetic); Bt crops would not be permitted for use. One concern about widespread use of transgenic Bt crops is the potential loss of the effectiveness of a relatively benign "biopesticide" if targeted insect pests were to gain resistance to Bt due to widespread exposure.

Fish consumption has increased greatly worldwide since 1950. What role has aquaculture played in this? Where does aquaculture currently take place? What are some species that are currently farmed?

While wild harvest of fish increased continuously in the 60s and 70s, it has leveled off since the late 1980s. Farmed fish has taken off since about 1990 and is growing very rapidly. We (the U.S.) import most (84%) of the fish we eat; 40% of it is now farmed in aquaculture systems. Most of the world's aquaculture takes place in Asia. Currently farmed fish include: shellfish, salmon, atlantic halibut, cobia, grouper, hybrid striped bass, trout, summer flounder, cod, rainbow smelt, sea urchins, oyster, and others.

In your garden, you see a large green caterpillar feeding on your broccoli. You look more closely and see what looks like a little black wasp on top of the caterpillar. What do you think might be going on? is this something you want to encourage in your garden?

the little black wasp is a parasitoid. It's likely that she is laying her eggs in the caterpillar, and that when they hatch, the caterpillar will be consumed from the inside out) Since the caterpillar is eating your broccoli, you definitely want to encourage this parasitoid to lay a lot of eggs

Define 'integrated pest management'.

the use of different techniques in combination to manage pests emphasis on methods that are least harmful to environment+ most specific to the particular pest. TO do this, growers need to understand how each pest works; e.g. it's life cycle and how/when/where it causes damage.