3-SITIOS ARQUEOLOGICOS ANALIZADOS EN ESTA TESIS

What is a management plan?

• Suitable for mono-specific or multi-species infestations of alien plants • Based on reliable surveys and mapping of these infestations

• Aimed at systematic reduction of the infestations • Makes use of locally registered herbicides

• Integrated control comprises mechanical, chemical and biological control methods • Budgets are drawn up for the land managers

• Aims for the land managers to become competent and independent in alien plant control What are the advantages of following an ARS-PPRI management plan?

• Latest technology from international herbicide companies • Visible progress with alien plant control

• Scientifically and ecologically sound • Practical, affordable and flexible • Tailored to the land manager's needs Additional options offered by ARS-PPRI

• Two day training courses aimed at management level

• Two day training course aimed at unskilled and semi-skilled labour

• Weedout: Software program to aid decision making with control operations (pamphlet available from ARS-PPRI)

• Weedout containing land manager's data on alien plants • Financial projections to aid budgeting in future years

GROUP DISCUSSION

Charudattan Could you explain the associations between Eccritotarsus and Bellura and their host-water hyacinth? Are they new associations?

Neser To my knowledge Eccritotarsus and water hyacinth is not a new association; the insect was collected on water hyacinth. It is a small bug that lives precariously and it sucks the juice of the plant. I have one slide here which shows a little bit of the damage; I didn't come prepared to talk about the bug. This one is Bellura, the one of which we know so much about because it borrows down the crown of the plant and it leaves the plant progressively more damaged. It's a very large noctuid larva. I am not sure; the insect was originally described from Santa Catarina, in Brazil and was found only in Rio de Janeiro later and in Santa Catarina. It multiplies very, very rapidly in quarantine and all that we know is that it seems to feed also on Pontederia in our host testing. That is all we know at this stage .

Charudattan There appears to be some concern that Bellura densa may feed on

Colocasia esculentum, which is an economically important crop in many

parts of Africa and Asia.

Neser That was the first point that we thought would be a risk. Larvae transferred to Colocasia burrowed into the corms and feed on them. But newly hatched larvae has so far never survived on Colocasia. They are pushed out of the plant leaf tissue by mucilage and killed without fail. So we have not discarded Bellura so far. However, because it is a risk to

Colocasia, we are holding onto it as long as we can and continuing the

tests. I hope that we will find various other insects on water hyacinth. Orach-Meza There are two questions I would like to ask: the first is in connection with

the winter effect on the water hyacinth. What is the period during the course of the year when the plant is not growing at all? And secondly, what happens to the biological control agents during winter?

Neser The process sets in about April which is about late Autumn, until September/October. The growth of the plant stops in April and it resumes in October - the tenth month. So it is a long period. Cilliers and I have found that looking under the match dates ones near the crown you would still find Neochetina and Sameodes survive the winter. There are, of course, always a few plants sheltered amongst bushes along the edges that do survive. It isn't as if they are all killed or all affected that badly. The crowns of the plants remain alive and the water temperature does not go all that low. Cilliers thinks the temperature doesn't have a severe effect on

the insects, but I think that is debatable. We think that the affected plants die back and the plants affect the insects - this may have a very slowing effect on the weed.

Center Do plants that are weakened by the insects succumb to the colder temperatures?

Neser Cilliers finds that plants having larval tunnels present in plants those tend to die earlier than those without a lot of tunnels. So, she has been monitoring this and it seems that the weaker plants do die.

One thing that I would like to comment on is this: we make the assumption that it is best to spray the water hyacinth as late as possible in the season, when the majority of the population of weevils will be in the adult stage. So we try and not do any chemical control until February, which is quite late in the summer, instead of spraying early in the season when water hyacinth is still in the initial phases of build-up. And this is based on a gut feeling because glyphosate apparently is not harmful to adults. I have no idea when one has N. bruchi and N. eichhorniae mixed and the populations go up and down in 1, 2 and 3 generations. That is something that one will have to look at when the plants are being sprayed. Because our aim is to recommend to the department of water affairs to spray only 75% of an infestation and always leave the other 25% edge unsprayed as a reservoir for insects. That is what we hoped to do and allow the insects to migrate, but whether they migrate or not, I don't know.

WATER HYACINTH: ITS PROBLEMS