Archive for September, 2009

Control of wild herbs with hot steam

Sunday, September 27th, 2009

The public sector, such as communities, must also deal with solutions to control wild herbs and weeds.

On squares, streets and sidewalks, weeds amass in gaps and free areas and have to be eliminated. Furthermore, challenges arise due to the steady spread of problematic plants such as the invasion of neophytes.

Invasive Neophytes and other problematic plants

In recent decades many non native plants have been introduced to Central Europe.

Many of these plants cause growing problems due to their rapid growth. Some are harmful to health such as Ambrosia, while others endanger biodiversity since they supplant native plant varieties and detriment the natural habitat. Among these is Japanese knotweed (Fallopia Japonica /Reynoutria Japonica) whose powerful growth suppresses other plants and depending on its location may damage agricultural land or building structures such as dams, streets and walls.

Furthermore, native problematic plants are further advancing such as ragwort which is toxic and can lead to liver damage and even fatal poisoning depending on the ingested dosage. The accelerated spread of ragwort can be traced back to growing area of fallow land and climate change.

In particular the public sector is faced with the challenges to address this issue.

Today two methods are applied for weed control: 1. Mechanical means such as brushing, mulching, bunking and mowing 2. Application of herbicides. In particular the usage of chemical means is limited due to its harmful impact on nature and humans.

Hot steam is an adequate alternative.

Steaming systems for weed control in public spaces are available and can universally be applied. In contrast to mechanical methods, which are quick and simple, steaming provides the advantage that not only superficial plant parts are removed. Hot steam penetrates into all gaps and fights the complete plant. It kills all sprouted plant parts and weed seeds making it really worth the effort. The results are completely weed-free areas which only require to be retreated once or twice a year. No chemicals are needed and the treatment is residue-free.

Steaming and other thermal methods.

Besides hot steam there are other thermal methods used for weed control available on the market such as infrared rays, scarfing and hotwater systems. The efficacy of these methods is often insufficient despite their relatively high energy usage. Radiant heaters preserve surfaces but require long residence times until heat has sufficiently damaged the plant in particular reaching parts underground. Scarfing devices have the same problem, since they show little depth effect.

Hotwater systems may overcome these issues. When applied properly, these systems can kill deeper sprouted plant parts at temperatures higher than 65°C for a positive long term effect. However hotwater systems show high energy losses and massive water consumption. Hot steam does not have these disadvantages.

More than „Hot air“

In contrast to hot water at 100°C, hot steam at 100°C contains about 5 times more energy. Furthermore its density is 1000 times lower. Hence when using hot steam, users need less water and can apply more heat to fight weeds: The result are weed-free areas at relatively low energy and labor cost. Furthermore, low pressure steam generators are very easy to handle.

In contrast to methods using extreme heat and high pressure the application of steam has more positive effects: Soil surface is preserved and freed from weeds, moss and linchen. Steaming even cleans deeper soil layers. Persistent dirt such as gum, etc. is loosened and can be removed easily after steaming.

Steaming systems are suitable for small as well as large areas with different surfaces such as sports and playgrounds, sidewalks, parking lots and cemeteries.

Steam can be applied anywhere.

Steam can be applied in many different areas. Communities can use steam generators not only for effective weed control and cleaning of squares and streets. Steaming systems can also be used to treat municipal green areas, beets and compost or zoological gardens. If coordinated and applied properly a steam generator never stands still.

Hohenheim Univeristy confirms the high effectiveness of steam against weeds at the 32nd horticulture day

Sunday, September 20th, 2009

On the 19.09.2009 (32nd horticulture day) Hohenheim University located close to Stuttgart presented the results of open field tests for weed control.

From June to September 2009 three methods of weed control were tested 4 times repeatedly on parcels of 16m x 1.2 m. On the parcels two Baby-Leaf salads “Batavia red” and “Batavia green” were planted.

The total testing area was divided into 18 plots, on which the three methods were compared with each other: weed control with pick, with herbicide and with soil steaming.

Steaming took place once before seeding after sufficient soil loosening, while herbicides were applied after seeding. Manual seed control with pick took place when weeds started to occur. Control plots were not subject to any weed control means.

Baby-Leaf cultures were harvested after 4 weeks. Then freshmass and drymass of salad and weed of all three test variations were measured and compared (steaming, herbicide, pick).

University Hohenheim yielded the result that after the application of 90°C hot steam, no weeds grew in the cultivation period. On sufficiently steamed areas weed control of Baby-Leaf-Cultures is not necessary.

Nitrate and Ammonium

As expected when examining the steamed soil, a relatively high but harmless concentration of ammonium and after harvest a high concentration of nitrate was measured due to the blocking of nitrifying bacteria through steaming. Ammonifying bacteria however were less affected through hot steam. Hence ammonia accumulates in steamed soil. More detailed results were yielded by S.N. Malowany and I.D. Newston in the middle of the last century already. Normally the ammonia / nitrate ratio normalizes within 6-8 weeks after steaming. This period can be significantly shortened if nitrifying and ammonifying bacteria are injected into the soil right after steaming(Integrated Steaming).

Practical experience of weed seed control with hot steam in horticulture

Sunday, September 13th, 2009

Since the middle of the last century, the effectiveness of humid heat to fight weeds, in particular their seeds, has been researched thoroughly. Within just 5 minutes all seeds can be rendered ungerminable as long as hot steam of 95°C is used steadily.

In practice today there is a trend of shorter treatments with hot steam in particular when fighting weed seeds on open fields. In particular in France, the Netherlands and in Denmark big areas of beet cultures are superficially sterilized to up to 5-10 cm depth using steaming automats. Special hoods with a total area of up to 20 square meters are moved step by step after just 5 minutes of steam injection.

The goal of using short steaming periods however is not the total abolition of resistant pathogens. Here longer steaming times and larger steaming depths are necessary. Instead the focus is the killing of weed seeds on the surface in order to give beet cultures a headstart so they can prevail against other growing weeds.

The results show success. Despite short steaming periods, hot steam can sufficiently harm seeds sufficiently to avoid the penetration of weeds.

This steaming method for superficial seed control is further propagated in Germany as well. This development can be traced back to the lack of available alternatives. In earlier times chemical means were used which are meanwhile prohibited or considered risky.

Furthermore the present discussion about the spread of ragwort and similar plant types drives the promotion of steaming. The market demands even more weed=free products, but due to the market price situation there is no alternative for automatic harvest methods. Hence, beets need to be free of weeds when harvesting.

Steaming as ecological method for seed control gains importance nationally as well as internationally.

Steaming against weeds and weed seeds

Wednesday, September 2nd, 2009

For more than 50 years the effect of heat on the germination capacity of weed seeds has been studied intensely.

Studies consider the effect on wet as well as dry seeds of different weed types, in which they were exposed to dry as well as humid heat such as hot steam for different durations. Studies made at the University of Zurich in the fifties of the last century showed clear results:

While dry heat did not yield a sufficient desired effect on seeds, humid heat such as hot steam ensured the complete killing of all seeds at 95°C after 5 minutes of treatment.

Dry heat even proved to be counterproductive: Germination capacity of weed seeds was even found to improve at times.
Hot steam showed to be the most thorough and effective means to treat against weed seeds and is superior to all other thermical methods as well has chemical herbicides, which are only partially effective against seeds.